______________________________________________________________________ 27 Input/output library [lib.input.output] ______________________________________________________________________ 1 This clause describes components that C++ programs may use to perform input/output operations. 2 The following subclauses describe requirements for stream parameters, and components for forward declarations of iostreams, predefined iostreams objects, base iostreams classes, stream buffering, stream formatting and manipulators, string streams, and file streams, as sum- marized in Table 1: Table 1--Input/output library summary +----------------------------------------------------------------+ | Subclause Header(s) | +----------------------------------------------------------------+ |_lib.iostreams.requirements_ Requirements | +----------------------------------------------------------------+ |_lib.iostream.forward_ Forward declarations <iosfwd> | +----------------------------------------------------------------+ |_lib.iostream.objects_ Standard iostream objects <iostream> | +----------------------------------------------------------------+ |_lib.iostreams.base_ Iostreams base classes <ios> | +----------------------------------------------------------------+ |_lib.stream.buffers_ Stream buffers <streambuf> | +----------------------------------------------------------------+ | <istream> | |_lib.iostream.format_ Formatting and manipulators <ostream> | | <iomanip> | +----------------------------------------------------------------+ |_lib.string.streams_ String streams <sstream> | | <cstdlib> | +----------------------------------------------------------------+ | <fstream> | |_lib.file.streams_ File streams <cstdio> | | <cwchar> | +----------------------------------------------------------------+ 27.1 Iostreams requirements [lib.iostreams.requirements] 27.1.1 Definitions [lib.iostreams.definitions] 1 For character-related definitions, see _lib.char.traits.defs_. Addi- tional iostreams definitions: --iostream class templates The iostream class templates are templates defined in this clause that take two template arguments: charT and traits. The argument charT is a character container class, and the argument traits is a structure which defines additional characteris- tics and functions of the character type represented by charT neces- sary to implement the iostream class templates. --narrow-oriented iostream classes The narrow-oriented iostream classes are the instantiations of the iostream class templates on the character container class char and the default value of the traits parameter. The traditional iostream classes are regarded as the narrow-oriented iostream classes (_lib.narrow.stream.objects_). --wide-oriented iostream classes The wide-oriented iostream classes are the instantiations of the iostream class templates on the char- acter container class wchar_t and the default value of the traits parameter. (_lib.wide.stream.objects_). --repositional streams and arbitrary-positional streams A repositional stream, can seek to only the position where we previously encoun- tered. On the other hand, an arbitrary-positional stream can seek to any integral position within the length of the stream. Every arbitrary-positional stream is repositional. 27.1.2 Limitations [lib.iostream.limits] 27.1.2.1 Imbue Limitations [lib.iostream.limits.imbue] No function described in clause _lib.input.output_ except for ios_base::imbue causes any instance of basic_ios::imbue or basic_streambuf::imbue to be called. If any user function called from a function declared in clause _lib.input.output_ or as an overriding virtual function of any class declared in clause _lib.input.output_ calls imbue the behavior is undefined. 27.1.2.2 Positioning Type Limitations [lib.iostreams.limits.pos] The classes of clause _lib.input.output_ with template arguments charT and traits behave as described if traits::pos_type and traits::off_type are streampos and streamoff respectively. Except as noted explicitly below their behavior when traits::pos_type and traits::off_type are other types are implementation-defined. 27.2 Forward declarations [lib.iostream.forward] Header <iosfwd> synopsis namespace std { templates template<class charT> class char_traits; template<> class char_traits<char>; template<> class char_traits<wchar_t>; template<class T> class allocator; template <class charT, class traits = char_traits<charT> > class basic_ios; template <class charT, class traits = char_traits<charT> > class basic_streambuf; template <class charT, class traits = char_traits<charT> > class basic_istream; template <class charT, class traits = char_traits<charT> > class basic_ostream; template <class charT, class traits = char_traits<charT> > class basic_iostream; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringbuf; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_istringstream; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_ostringstream; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringstream; template <class charT, class traits = char_traits<charT> > class basic_filebuf; template <class charT, class traits = char_traits<charT> > class basic_ifstream; template <class charT, class traits = char_traits<charT> > class basic_ofstream; template <class charT, class traits = char_traits<charT> > class basic_fstream; template <class charT, class traits = char_traits<charT> > class basic_istreambuf_iterator; template <class charT, class traits = char_traits<charT> > class basic_ostreambuf_iterator; typedef basic_ios<char> ios; typedef basic_ios<wchar_t> wios; typedef basic_streambuf<char> streambuf; typedef basic_istream<char> istream; typedef basic_ostream<char> ostream; typedef basic_iostream<char> iostream; typedef basic_stringbuf<char> stringbuf; typedef basic_istringstream<char> istringstream; typedef basic_ostringstream<char> ostringstream; typedef basic_stringstream<char> stringstream; typedef basic_filebuf<char> filebuf; typedef basic_ifstream<char> ifstream; typedef basic_ofstream<char> ofstream; typedef basic_fstream<char> fstream; typedef basic_streambuf<wchar_t> wstreambuf; typedef basic_istream<wchar_t> wistream; typedef basic_ostream<wchar_t> wostream; typedef basic_iostream<wchar_t> wiostream; typedef basic_stringbuf<wchar_t> wstringbuf; typedef basic_istringstream<wchar_t> wistringstream; typedef basic_ostringstream<wchar_t> wostringstream; typedef basic_stringstream<wchar_t> wstringstream; typedef basic_filebuf<wchar_t> wfilebuf; typedef basic_ifstream<wchar_t> wifstream; typedef basic_ofstream<wchar_t> wofstream; typedef basic_fstream<wchar_t> wfstream; template <class state> class fpos; typedef fpos<char_traits<char>::state_type> streampos; typedef fpos<char_traits<wchar_t>::state_type> wstreampos; } +------- BEGIN BOX 1 -------+ streamoff here? +------- END BOX 1 -------+ [Note: 1 The template class basic_ios<charT,traits> serves as a virtual base class for the classes basic_istream<charT,traits>, basic_ostream<charT,traits>, and classes derived from them. basic_iostream<charT,traits> is a class derived from both basic_istream and basic_ostream. 2 The template class basic_streambuf<charT,traits> serves as a base class for template classes basic_stringbuf, and basic_filebuf. 3 The template class basic_istream serves as a base class for template classes basic_istringstream, and basic_ifstream 4 The template class basic_ostream serves as a base class for template classes basic_ostringstream, and basic_ofstream 5 The template class basic_iostream serves as a base class for template classes basic_stringstream, and basic_fstream. 6 Other typedefs define instances of template classes specialized for char or wchar_t types. 7 The template class fpos<charT> is a class used for specifying file position information. 8 The types streampos and wstreampos are used for positioning streams specialized on char and wchar_t respectively. 9 This synopsis suggests a circularity between streampos and char_traits<char>. An implementation can avoid this circularity by substituting equivalent types. One way to do this might be template<class stateT> class fpos { ... }; // depends on nothing typedef ... _STATE; // implementation private declaration of stateT typedef fpos<_STATE> streampos; template<> struct char_traits<char> { typedef streampos pos_type; // ... } --end note] 27.3 Standard iostream objects [lib.iostream.objects] Header <iostream> synopsis namespace std { extern istream cin; extern ostream cout; extern ostream cerr; extern ostream clog; extern wistream wcin; extern wostream wcout; extern wostream wcerr; extern wostream wclog; } 1 The header <iostream> declares objects that associate objects with the standard C streams provided for by the functions declared in <cstdio> (_lib.c.files_). 2 Mixing operations on corresponding wide- and narrow-character streams follows the same semantics as mixing such operations on FILEs, as specified in Amendment 1 of the ISO C standard. The objects are con- structed, and the associations are established at some time prior to or during first time an object of class basic_ios<charT,traits>::Init is constructed, and in any case before the body of main begins execution.1) The objects are not destroyed during program execution.2) _________________________ 1) If it is possible for them to do so, implementations are encouraged to initialize the objects earlier than required. 2) Constructors and destructors for static objects can access these objects to read input from stdin or write output to stdout or stderr. 27.3.1 Narrow stream objects [lib.narrow.stream.objects] istream cin; 1 The object cin controls input from a stream buffer associated with the object stdin, declared in <cstdio>. 2 After the object cin is initialized, cin.tie() returns &cout. Its state is otherwise the same as required for ios_base::init (_lib.basic.ios.cons_). ostream cout; 3 The object cout controls output to a stream buffer associated with the object stdout, declared in <cstdio> (_lib.c.files_). ostream cerr; 4 The object cerr controls output to a stream buffer associated with the object stderr, declared in <cstdio> (_lib.c.files_). 5 After the object cerr is initialized, cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (_lib.basic.ios.cons_). ostream clog; 6 The object clog controls output to a stream buffer associated with the object stderr, declared in <cstdio> (_lib.c.files_). 27.3.2 Wide stream objects [lib.wide.stream.objects] wistream wcin; 1 The object wcin controls input from a stream buffer associated with the object stdin, declared in <cstdio>. 2 After the object wcin is initialized, wcin.tie() returns &wcout. Its state is otherwise the same as required for ios_base::init (_lib.basic.ios.cons_). wostream wcout; 3 The object wcout controls output to a stream buffer associated with the object stdout, declared in <cstdio> (_lib.c.files_). wostream wcerr; 4 The object wcerr controls output to a stream buffer associated with the object stderr, declared in <cstdio> (_lib.c.files_). 5 After the object wcerr is initialized, wcerr.flags() & unitbuf is nonzero. Its state is otherwise the same as required for ios_base::init (_lib.basic.ios.cons_). wostream wclog; 6 The object wclog controls output to a stream buffer associated with the object stderr, declared in <cstdio> (_lib.c.files_). 27.4 Iostreams base classes [lib.iostreams.base] Header <ios> synopsis #include <iosfwd> namespace std { typedef OFF_T streamoff; typedef SZ_T streamsize; template <class stateT> class fpos; class ios_base; template <class charT, class traits = char_traits<charT> > class basic_ios; // _lib.std.ios.manip_, manipulators: ios_base& boolalpha (ios_base& str); ios_base& noboolalpha(ios_base& str); ios_base& showbase (ios_base& str); ios_base& noshowbase (ios_base& str); ios_base& showpoint (ios_base& str); ios_base& noshowpoint(ios_base& str); ios_base& showpos (ios_base& str); ios_base& noshowpos (ios_base& str); ios_base& skipws (ios_base& str); ios_base& noskipws (ios_base& str); ios_base& uppercase (ios_base& str); ios_base& nouppercase(ios_base& str); // _lib.adjustfield.manip_ adjustfield: ios_base& internal (ios_base& str); ios_base& left (ios_base& str); ios_base& right (ios_base& str); // _lib.basefield.manip_ basefield: ios_base& dec (ios_base& str); ios_base& hex (ios_base& str); ios_base& oct (ios_base& str); // _lib.floatfield.manip_ floatfield: ios_base& fixed (ios_base& str); ios_base& scientific (ios_base& str); } 27.4.1 Types [lib.stream.types] typedef OFF_T streamoff; 1 The type streamoff is an implementation-defined type that satisfies the requirements of _lib.fpos.operations_. typedef SZ_T streamsize; 2 The type streamsize is a synonym for one of the signed basic integral types. It is used to represent the number of characters transferred in an I/O operation, or the size of I/O buffers.3) 27.4.2 Class ios_base [lib.ios.base] namespace std { class ios_base { public: class failure; _________________________ 3) streamsize is used in most places where ISO C would use size_t. Most of the uses of streamsize could use size_t, except for the strstreambuf constructors, which require negative values. It should probably be the signed type corresponding to size_t (which is what Posix.2 calls ssize_t). typedef T1 fmtflags; static const fmtflags boolalpha; static const fmtflags dec; static const fmtflags fixed; static const fmtflags hex; static const fmtflags internal; static const fmtflags left; static const fmtflags oct; static const fmtflags right; static const fmtflags scientific; static const fmtflags showbase; static const fmtflags showpoint; static const fmtflags showpos; static const fmtflags skipws; static const fmtflags unitbuf; static const fmtflags uppercase; static const fmtflags adjustfield; static const fmtflags basefield; static const fmtflags floatfield; typedef T2 iostate; static const iostate badbit; static const iostate eofbit; static const iostate failbit; static const iostate goodbit; typedef T3 openmode; static const openmode app; static const openmode ate; static const openmode binary; static const openmode in; static const openmode out; static const openmode trunc; typedef T4 seekdir; static const seekdir beg; static const seekdir cur; static const seekdir end; class Init; // _lib.fmtflags.state_ fmtflags state: fmtflags flags() const; fmtflags flags(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl); fmtflags setf(fmtflags fmtfl, fmtflags mask); void unsetf(fmtflags mask); streamsize precision() const; streamsize precision(streamsize prec); streamsize width() const; streamsize width(streamsize wide); // _lib.ios.base.locales_ locales: locale imbue(const locale& loc); locale getloc() const; // _lib.ios.base.storage_ storage: static int xalloc(); long& iword(int index); void*& pword(int index); // destructor virtual ~ios_base(); // _lib.ios.base.callback_ callbacks; enum event { erase_event, imbue_event, copyfmt_event }; typedef void (*event_callback)(event, ios_base&, int index) throw(); void register_callback(event_call_back fn, int index); static bool sync_with_stdio(bool sync = true); protected: ios_base(); private: // static int index; exposition only // long* iarray; exposition only // void** parray; exposition only }; } 1 ios_base defines several member types: --a class failure derived from exception; --a class Init; --three bitmask types, fmtflags, iostate, and openmode; --an enumerated type, seekdir. 2 It maintains several kinds of data: --state information that reflects the integrity of the stream buffer; --control information that influences how to interpret (format) input sequences and how to generate (format) output sequences; --additional information that is stored by the program for its private use. 3 [Note: For the sake of exposition, the maintained data is presented here as: --static int index, specifies the next available unique index for the integer or pointer arrays maintained for the private use of the pro- gram, initialized to an unspecified value; --long* iarray, points to the first element of an arbitrary-length long array maintained for the private use of the program; --void** parray, points to the first element of an arbitrary-length pointer array maintained for the private use of the program. --end note] 27.4.2.1 Types [lib.ios.types] 27.4.2.1.1 Class ios_base::failure [lib.ios::failure] namespace std { class ios_base::failure : public exception { public: explicit failure(const string& msg); virtual ~failure(); virtual const char* what() const throw(); }; } 1 The class failure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations. explicit failure(const string& msg); Effects: Constructs an object of class failure, initializing the base class with exception(msg). Postcondition: strcmp(what(), msg.c_str()) == 0 const char* what() const; Returns: The message msg with which the exception was created. 27.4.2.1.2 Type ios_base::fmtflags [lib.ios::fmtflags] typedef T1 fmtflags; 1 The type fmtflags is a bitmask type (_lib.bitmask.types_). Setting its elements has the effects indicated in Table 2: Table 2--fmtflags effects +-----------------------------------------------------------+ | Element Effect(s) if set | +-----------------------------------------------------------+ |boolalpha insert and extract bool type in alphabetic | | format | |dec converts integer input or generates integer | | output in decimal base | |fixed generate floating-point output in fixed-point | | notation; | |hex converts integer input or generates integer | | output in hexadecimal base; | |internal adds fill characters at a designated internal | | point in certain generated output, or identi- | | cal to right if no such point is designated; | |left adds fill characters on the right (final po- | | sitions) of certain generated output; | |oct converts integer input or generates integer | | output in octal base; | |right adds fill characters on the left (initial po- | | sitions) of certain generated output; | |scientific generates floating-point output in scientific | | notation; | |showbase generates a prefix indicating the numeric | | base of generated integer output; | |showpoint generates a decimal-point character uncondi- | | tionally in generated floating-point output; | |showpos generates a + sign in non-negative generated | | numeric output; | |skipws skips leading white space before certain in- | | put operations; | |unitbuf flushes output after each output operation; | |uppercase replaces certain lowercase letters with their | | uppercase equivalents in generated output. | +-----------------------------------------------------------+ 2 Type fmtflags also defines the constants indicated in Table 3: Table 3--fmtflags constants ---------------------------------------- Constant Allowable values ---------------------------------------- adjustfield left | right | internal basefield dec | oct | hex floatfield scientific | fixed ---------------------------------------- | | | | | | | | | | 27.4.2.1.3 Type ios_base::iostate [lib.ios::iostate] typedef T2 iostate; 1 The type iostate is a bitmask type (_lib.bitmask.types_) that contains the elements indicated in Table 4: Table 4--iostate effects +--------------------------------------------------------+ |Element Effect(s) if set | +--------------------------------------------------------+ |badbit indicates a loss of integrity in an input or | | output sequence (such as an irrecoverable | | read error from a file); | |eofbit indicates that an input operation reached the | | end of an input sequence; | |failbit indicates that an input operation failed to | | read the expected characters, or that an out- | | put operation failed to generate the desired | | characters. | +--------------------------------------------------------+ 2 Type iostate also defines the constant: --goodbit, the value zero. 27.4.2.1.4 Type ios_base::openmode [lib.ios::openmode] typedef T3 openmode; 1 The type openmode is a bitmask type (_lib.bitmask.types_). It con- tains the elements indicated in Table 5: Table 5--openmode effects +---------------------------------------------------+ |Element Effect(s) if set | +---------------------------------------------------+ |app seek to end before each write | |ate open and seek to end immediately after | | opening | |binary perform input and output in binary mode | | (as opposed to text mode) | |in open for input | |out open for output | |trunc truncate an existing stream when opening | +---------------------------------------------------+ 27.4.2.1.5 Type ios_base::seekdir [lib.ios::seekdir] typedef T4 seekdir; 1 The type seekdir is an enumerated type (_lib.enumerated.types_) that contains the elements indicated in Table 6: Table 6--seekdir effects +----------------------------------------------------------+ |Element Meaning | +----------------------------------------------------------+ |beg request a seek (for subsequent input or output) | | relative to the beginning of the stream | |cur request a seek relative to the current position | | within the sequence | |end request a seek relative to the current end of | | the sequence | +----------------------------------------------------------+ 27.4.2.1.6 Class ios_base::Init [lib.ios::Init] namespace std { class ios_base::Init { public: Init(); ~Init(); private: // static int init_cnt; exposition only }; } 1 The class Init describes an object whose construction ensures the con- struction of the eight objects declared in <iostream> (_lib.iostream.objects_) that associate file stream buffers with the standard C streams provided for by the functions declared in <cstdio> (_lib.c.files_). 2 For the sake of exposition, the maintained data is presented here as: --static int init_cnt, counts the number of constructor and destructor calls for class Init, initialized to zero. Init(); Effects: Constructs an object of class Init. If init_cnt is zero, the func- tion stores the value one in init_cnt, then constructs and initial- izes the objects cin, cout, cerr, clog (_lib.nar- row.stream.objects_), wcin, wcout, wcerr, and wclog (_lib.wide.stream.objects_). In any case, the function then adds one to the value stored in init_cnt. ~Init(); Effects: Destroys an object of class Init. The function subtracts one from the value stored in init_cnt and, if the resulting stored value is one, calls cout.flush(), cerr.flush(), clog.flush(), wcout.flush(), wcerr.flush(), wclog.flush(). 27.4.2.2 ios_base fmtflags state functions [lib.fmtflags.state] fmtflags flags() const; Returns: The format control information for both input and output. fmtflags flags(fmtflags fmtfl); Postcondition: fmtfl == flags(). Returns: The previous value of flags(). fmtflags setf(fmtflags fmtfl); Effects: Sets fmtfl in flags(). Returns: The previous value of flags(). fmtflags setf(fmtflags fmtfl, fmtflags mask); Effects: Clears mask in flags(), sets fmtfl & mask in flags(). Returns: The previous value of flags(). void unsetf(fmtflags mask); Effects: Clears mask in flags(). streamsize precision() const; Returns: The precision (number of digits after the decimal point) to generate on certain output conversions. streamsize precision(streamsize prec); Postcondition: prec == precision(). Returns: The previous value of precision(). streamsize width() const; Returns: The minimum field width (number of characters) to generate on cer- tain output conversions. streamsize width(streamsize wide); Postcondition: wide == width(). Returns: The previous value of width(). 27.4.2.3 ios_base locale functions [lib.ios.base.locales] locale imbue(const locale loc); Effects: Calls each registered callback pair (fn,index) (_lib.ios.base.call- back_) as (*fn)(imbue_event,*this,index) at such a time that a call to ios_base::getloc() from within fn returns the new locale value loc. Returns: If no locale has been imbued, a copy of the global C++ locale, locale(), in effect at the time of construction. Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations Postcondition: loc == getloc(). locale getloc() const; Returns: The previous value of getloc(). 27.4.2.4 ios_base static members [lib.ios.members.static] bool sync_with_stdio(bool sync = true); Returns: true, the first time it is called; otherwise, returns true if the standard iostream objects (_lib.iostream.objects_) are synchronized and otherwise returns false. Effects: If any input or output operation has occurred using the standard streams prior to the call, the effect is implementation-defined. Otherwise, called with a false argument, it allows the standard streams to operate independently of the standard C streams. +------- BEGIN BOX 2 -------+ "independent operation" may be need a more careful definition. +------- END BOX 2 -------+ 27.4.2.5 ios_base storage functions [lib.ios.base.storage] static int xalloc(); Returns: index ++. long& iword(int idx); Effects: If iarray is a null pointer, allocates an array of long of unspeci- fied size and stores a pointer to its first element in iarray. The function then extends the array pointed at by iarray as necessary to include the element iarray[idx]. Each newly allocated element of the array is initialized to zero. The reference returned may become invalid after another call to the object's iword member with a dif- ferent index, after a call to its copyfmt member, or when the object is destroyed.4) If the function fails5) it sets badbit, which may throw an exception. Returns: On success iarray[idx]. On failure, a valid long& initialized to 0. void* & pword(int idx); Effects: If parray is a null pointer, allocates an array of pointers to void of unspecified size and stores a pointer to its first element in parray. The function then extends the array pointed at by parray as necessary to include the element parray[idx]. Each newly allocated element of the array is initialized to a null pointer. The refer- ence returned may become invalid after another call to the object's pword member with a different index, after call to its copyfmt mem- ber, or when the object is destroyed. If the function fails6) it sets badbit, which may throw an exception. Returns: On success parray[idx]. On failure a valid void*& initialized to 0. Notes: After a subsequent call to pword(int) for the same object, the ear- lier return value may no longer be valid. _________________________ 4) An implementation is free to implement both the integer array pointed at by iarray and the pointer array pointed at by parray as sparse data structures, possibly with a one-element cache for each. 5) for example, because it cannot allocate space. 6) for example, because it cannot allocate space. 27.4.2.6 ios_base callbacks [lib.ios.base.callback] void register_callback(event_callback fn, int index); Effects: Registers the pair (fn,index) such that during calls to imbue() (_lib.ios.base.locales_), copyfmt(), or ~ios_base() (_lib.ios.base.cons_), the function fn is called with argument index. Functions registered are called when an event occurs, in opposite order of registration. Functions registered while a call- back function is active are not called until the next event. Notes: Identical pairs are not merged. A function registered twice will be called twice. 27.4.2.7 ios_base constructors/destructors [lib.ios.base.cons] ios_base(); Effects: Each ios_base member has an indeterminate value after construction. ~ios_base() Effects: Destroys an object of class ios_base. Calls each registered call- back pair (fn,index) (_lib.ios.base.callback_) as (*fn)(erase_event,*this,index) at such time that any ios_base member function called from within fn has well defined results. 27.4.3 Template class fpos [lib.fpos] namespace std { template <class stateT> class fpos { public: // _lib.fpos.cons_ Constructors explicit fpos(stateT); // _lib.fpos.members_ Members stateT state() const; void state(stateT); private; stateT st; // exposition only }; } 27.4.3.1 fpos Constructor [lib.fpos.cons] fpos(stateT s) Effects: Constructs an object and assigns s to st [Note: An fpos will also contain private information needed to position a file. This infor- mation is initialized in an unspecified fashion. --end note] 27.4.3.2 fpos Members [lib.fpos.members] void state(stateT s); Effects: Assign s to st. stateT state(); Returns: Current value of st. 27.4.4 fpos requirements [lib.fpos.operations] 1 Operations specified in Table 7 are permitted. In that table, --P refers to an instance of fpos, --p and q refer to an values of type P, --O refers to type streamoff, --o refers to a value of type streamoff, --sz refers to a value of type streamsize and --i refers to a value of type int. Table 7--Position type requirements +--------------------------------------------------------------------------------------------+ | expression return type operational assertion/note | | semantics pre/post-condition | +--------------------------------------------------------------------------------------------+ |P(i) p == P(i) | | note: a destructor is assumed. | +--------------------------------------------------------------------------------------------+ |P p(i); | |P p = i; post: p == P(i). | +--------------------------------------------------------------------------------------------+ |P(o) fpos converts from offset | +--------------------------------------------------------------------------------------------+ |O(p) OFF_T converts to offset P(O(p)) == p | +--------------------------------------------------------------------------------------------+ |p == q convertible to bool == is an equivalence relation | +--------------------------------------------------------------------------------------------+ |p != q convertible to bool !(p==q) | +--------------------------------------------------------------------------------------------+ |q = p + o fpos + offset q-o == p | |p += o | +--------------------------------------------------------------------------------------------+ |q = p - o fpos - offset q+o == p | |p -= o | +--------------------------------------------------------------------------------------------+ |o = p - q OFF_T distance q+o == p | +--------------------------------------------------------------------------------------------+ |streamsize(o) streamsize converts streamsize(O(sz)) == sz | |O(sz) OFF_T converts streamsize(O(sz)) == sz | +--------------------------------------------------------------------------------------------+ +--------------------------------------------------------------------------------------------+ [Note: Every implementation is required to supply overloaded opera- tors on fpos objects to satisfy the requirements of _lib.fpos.opera- tions_. It is unspecified whether these operators are members of fpos, global operators, or provided in some other way. --end note] 2 Stream operations that return a value of type traits::pos_type return P(O(-1)) as an invalid value to signal an error. If this value is used as an argument to any istream, ostream, or streambufmember that accepts a value of type traits::pos_type then the behavior of that function is undefined. 27.4.5 Template class basic_ios [lib.ios] namespace std { template <class charT, class traits = char_traits<charT> > class basic_ios : public ios_base { public: // Types: typedef charT char_type; typedef typename traits::int_type int_type; typedef typename traits::pos_type pos_type; typedef typename traits::off_type off_type; typedef traits traits_type; operator void*() const bool operator!() const iostate rdstate() const; void clear(iostate state = goodbit); void setstate(iostate state); bool good() const; bool eof() const; bool fail() const; bool bad() const; iostate exceptions() const; void exceptions(iostate except); // _lib.basic.ios.cons_ Constructor/destructor: explicit basic_ios(basic_streambuf<charT,traits>* sb); virtual ~basic_ios(); // _lib.basic.ios.members_ Members: basic_ostream<charT,traits>* tie() const; basic_ostream<charT,traits>* tie(basic_ostream<charT,traits>* tiestr); basic_streambuf<charT,traits>* rdbuf() const; basic_streambuf<charT,traits>* rdbuf(basic_streambuf<charT,traits>* sb); basic_ios& copyfmt(const basic_ios& rhs); char_type fill() const; char_type fill(char_type ch); // _lib.ios.base.locales_ locales: locale imbue(const locale& loc); char narrow(char_type c, char dfault) const; char_type widen(char c) const; protected: basic_ios(); void init(basic_streambuf<charT,traits>* sb); private: basic_ios(const basic_ios& ); // not defined basic_ios& operator=(const basic_ios&); // not defined }; } 27.4.5.1 basic_ios constructors [lib.basic.ios.cons] explicit basic_ios(basic_streambuf<charT,traits>* sb); Effects: Constructs an object of class basic_ios, assigning initial values to its member objects by calling init(sb). basic_ios(); Effects: Constructs an object of class basic_ios (_lib.ios.base.cons_) leav- ing its member objects uninitialized. The object must be initialized by calling its init member function. If it is destroyed before it has been initialized the behavior is undefined. void init(basic_streambuf<charT,traits>* sb); Postconditions: The postconditions of this function are indicated in Table 8: Table 8--ios_base() effects +--------------------------------------------------------+ | Element Value | +--------------------------------------------------------+ |rdbuf() sb | |tie() 0 | |rdstate() goodbit if sb is not a null pointer, | | otherwise badbit. | |exceptions() goodbit | |flags() skipws | dec | |width() 0 | |precision() 6 | |fill() widen(' '); | |getloc() a copy of the value returned by locale() | |iarray a null pointer | |parray a null pointer | +--------------------------------------------------------+ 27.4.5.2 Member functions [lib.basic.ios.members] basic_ostream<charT,traits>* tie() const; Returns: An output sequence that is tied to (synchronized with) the sequence controlled by the stream buffer. basic_ostream<charT,traits>* tie(basic_ostream<charT,traits>* tiestr); Postcondition: tiestr == tie(). Returns: The previous value of tie(). basic_streambuf<charT,traits>* rdbuf() const; Returns: A pointer to the streambuf associated with the stream. basic_streambuf<charT,traits>* rdbuf(basic_streambuf<charT,traits>* sb); Postcondition: sb == rdbuf(). Effects: Calls clear(). Returns: The previous value of rdbuf(). // _lib.ios.base.locales_ locales: locale imbue(const locale& loc); Effects: Calls ios_base::imbue(loc) (_lib.ios.base.locales_) and if rdbuf()!=0 then rdbuf()->pubimbue(loc) (_lib.streambuf.locales_). Returns: The prior value of ios_base::imbue(). char narrow(char_type c, char dfault) const; Returns: use_facet< ctype<char_type> >(getloc()).narrow(c,dfault) char_type widen(char c) const; Returns: use_facet< ctype<char_type> >(getloc()).widen(c) char_type fill() const Returns: The character used to pad (fill) an output conversion to the speci- fied field width. char_type fill(char_type fillch); Postcondition: fillch == fill() Returns: The previous value of fill(). basic_ios& copyfmt(const basic_ios& rhs); Effects: Assigns to the member objects of *this the corresponding member objects of rhs, except that: --rdstate() and rdbuf() are left unchanged; --exceptions() is altered last by calling exceptions(rhs.except). --The contents of arrays pointed at by pword and iword are copied not the pointers themselves.7) 1 If any newly stored pointer values in *this point at objects stored outside the object rhs, and those objects are destroyed when rhs is destroyed, the newly stored pointer values are altered to point at newly constructed copies of the objects. 2 Before copying any parts of rhs, calls each registered callback pair (fn,index) as (*fn)(erase_event,*this,index). After all parts but exceptions() have been replaced, calls each callback pair that was copied from rhs as (*fn)(copy_event,*this,index). Notes: The second pass permits a copied pword value to be zeroed, or its referent deep copied or reference counted or have other special action taken. Returns: *this. 27.4.5.3 basic_ios iostate flags functions [lib.iostate.flags] operator void*() const Returns: If fail() then a null pointer; otherwise some non-null pointer to indicate success. bool operator!() const Returns: fail(). _________________________ 7) This suggests an infinite amount of copying, but the implementation can keep track of the maximum element of the arrays that is non-zero. iostate rdstate() const; Returns: The error state of the stream buffer. void clear(iostate state = goodbit); Postcondition: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==state|ios_base::badbit. Effects: If (rdstate() & exceptions()) == 0, returns. Otherwise, the func- tion throws an object fail of class basic_ios::failure (_lib.ios::failure_), constructed with implementation-defined argu- ment values. void setstate(iostate state); Effects: Calls clear(rdstate() | state) (which may throw basic_ios::failure (_lib.ios::failure_)). bool good() const; Returns: rdstate() == 0 bool eof() const; Returns: true if eofbit is set in rdstate(). bool fail() const; Returns: true if failbit or badbit is set in rdstate().8) bool bad() const; Returns: true if badbit is set in rdstate(). iostate exceptions() const; _________________________ 8) Checking badbit also for fail() is historical practice. Returns: A mask that determines what elements set in rdstate() cause excep- tions to be thrown. void exceptions(iostate except); Postcondition: except == exceptions(). Effects: Calls clear(rdstate()). 27.4.6 ios_base manipulators [lib.std.ios.manip] 27.4.6.1 fmtflags manipulators [lib.fmtflags.manip] ios_base& boolalpha(ios_base& str); Effects: Calls str.setf(ios_base::boolalpha). Returns: str. ios_base& noboolalpha(ios_base& str); Effects: Calls str.unsetf(ios_base::boolalpha). Returns: str. ios_base& showbase(ios_base& str); Effects: Calls str.setf(ios_base::showbase). Returns: str. ios_base& noshowbase(ios_base& str); Effects: Calls str.unsetf(ios_base::showbase). Returns: str. ios_base& showpoint(ios_base& str); Effects: Calls str.setf(ios_base::showpoint). Returns: str. ios_base& noshowpoint(ios_base& str); Effects: Calls str.unsetf(ios_base::showpoint). Returns: str. ios_base& showpos(ios_base& str); Effects: Calls str.setf(ios_base::showpos). Returns: str. ios_base& noshowpos(ios_base& str); Effects: Calls str.unsetf(ios_base::showpos). Returns: str. ios_base& skipws(ios_base& str); Effects: Calls str.setf(ios_base::skipws). Returns: str. ios_base& noskipws(ios_base& str); Effects: Calls str.unsetf(ios_base::skipws). Returns: str. ios_base& uppercase(ios_base& str); Effects: Calls str.setf(ios_base::uppercase). Returns: str. ios_base& nouppercase(ios_base& str); Effects: Calls str.unsetf(ios_base::uppercase). Returns: str. ios_base& unitbuf(ios_base& str); Effects: Calls str.setf(ios_base::unitbuf). Returns: str. ios_base& nounitbuf(ios_base& str); Effects: Calls str.unsetf(ios_base::unitbuf). Returns: str. 27.4.6.2 adjustfield manipulators [lib.adjustfield.manip] ios_base& internal(ios_base& str); Effects: Calls str.setf(ios_base::internal, ios_base::adjustfield). Returns: str. ios_base& left(ios_base& str); Effects: Calls str.setf(ios_base::left, ios_base::adjustfield). Returns: str. ios_base& right(ios_base& str); Effects: Calls str.setf(ios_base::right, ios_base::adjustfield). Returns: str. 27.4.6.3 basefield manipulators [lib.basefield.manip] ios_base& dec(ios_base& str); Effects: Calls str.setf(ios_base::dec, ios_base::basefield). Returns: str. ios_base& hex(ios_base& str); Effects: Calls str.setf(ios_base::hex, ios_base::basefield). Returns: str. ios_base& oct(ios_base& str); Effects: Calls str.setf(ios_base::oct, ios_base::basefield). Returns: str. 27.4.6.4 floatfield manipulators [lib.floatfield.manip] ios_base& fixed(ios_base& str); Effects: Calls str.setf(ios_base::fixed, ios_base::floatfield). Returns: str. ios_base& scientific(ios_base& str); Effects: Calls str.setf(ios_base::scientific, ios_base::floatfield). Returns: str. 27.5 Stream buffers [lib.stream.buffers] Header <streambuf> synopsis namespace std { template <class charT, class traits = char_traits<charT> > class basic_streambuf; typedef basic_streambuf<char> streambuf; typedef basic_streambuf<wchar_t> wstreambuf; } _________________________ 9) The function signature dec(ios_base&) can be called by the function signature basic_ostream& stream::operator<<(ios_base& (*)(ios_base&)) to permit expressions of the form cout << dec to change the format flags stored in cout. 1 The header <streambuf> defines types that control input from and out- put to character sequences. 27.5.1 Stream buffer requirements [lib.streambuf.reqts] 1 Stream buffers can impose various constraints on the sequences they control. Some constraints are: --The controlled input sequence can be not readable. --The controlled output sequence can be not writable. --The controlled sequences can be associated with the contents of other representations for character sequences, such as external files. --The controlled sequences can support operations directly to or from associated sequences. --The controlled sequences can impose limitations on how the program can read characters from a sequence, write characters to a sequence, put characters back into an input sequence, or alter the stream position. 2 Each sequence is characterized by three pointers which, if non-null, all point into the same charT array object. The array object repre- sents, at any moment, a (sub)sequence of characters from the sequence. Operations performed on a sequence alter the values stored in these pointers, perform reads and writes directly to or from associated sequences, and alter ``the stream position'' and conversion state as needed to maintain this subsequence relationship. The three pointers are: --the beginning pointer, or lowest element address in the array (called xbeg here); --the next pointer, or next element address that is a current candi- date for reading or writing (called xnext here); --the end pointer, or first element address beyond the end of the array (called xend here). 3 The following semantic constraints shall always apply for any set of three pointers for a sequence, using the pointer names given immedi- ately above: --If xnext is not a null pointer, then xbeg and xend shall also be non-null pointers into the same charT array, as described above; otherwise, xbeg and xend shall also be null. --If xnext is not a null pointer and xnext < xend for an output sequence, then a write position is available. In this case, *xnext shall be assignable as the next element to write (to put, or to store a character value, into the sequence). --If xnext is not a null pointer and xbeg < xnext for an input sequence, then a putback position is available. In this case, xnext[-1] shall have a defined value and is the next (preceding) element to store a character that is put back into the input sequence. --If xnext is not a null pointer and xnext < xend for an input sequence, then a read position is available. In this case, *xnext shall have a defined value and is the next element to read (to get, or to obtain a character value, from the sequence). 27.5.2 Template class [lib.streambuf] basic_streambuf<charT,traits> namespace std { template <class charT, class traits = char_traits<charT> > class basic_streambuf { public: // Types: typedef charT char_type; typedef typename traits::int_type int_type; typedef typename traits::pos_type pos_type; typedef typename traits::off_type off_type; typedef traits traits_type; virtual ~basic_streambuf(); // _lib.streambuf.locales_ locales: locale pubimbue(const locale &loc); locale getloc() const; // _lib.streambuf.buffer_ buffer and positioning: basic_streambuf<char_type,traits>* pubsetbuf(char_type* s, streamsize n); pos_type pubseekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); pos_type pubseekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); int pubsync(); // Get and put areas: // _lib.streambuf.pub.get_ Get area: streamsize in_avail(); int_type snextc(); int_type sbumpc(); int_type sgetc(); streamsize sgetn(char_type* s, streamsize n); // _lib.streambuf.pub.pback_ Putback: int_type sputbackc(char_type c); int_type sungetc(); // _lib.streambuf.pub.put_ Put area: int_type sputc(char_type c); streamsize sputn(const char_type* s, streamsize n); protected: basic_streambuf(); // _lib.streambuf.get.area_ Get area: char_type* eback() const; char_type* gptr() const; char_type* egptr() const; void gbump(int n); void setg(char_type* gbeg, char_type* gnext, char_type* gend); // _lib.streambuf.put.area_ Put area: char_type* pbase() const; char_type* pptr() const; char_type* epptr() const; void pbump(int n); void setp(char_type* pbeg, char_type* pend); // _lib.streambuf.virtuals_ virtual functions: // _lib.streambuf.virt.locales_ Locales: virtual void imbue(const locale &loc); // _lib.streambuf.virt.buffer_ Buffer management and positioning: virtual basic_streambuf<char_type,traits>* setbuf(char_type* s, streamsize n); virtual pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); virtual pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); virtual int sync(); // _lib.streambuf.virt.get_ Get area: virtual int showmanyc(); virtual streamsize xsgetn(char_type* s, streamsize n); virtual int_type underflow(); virtual int_type uflow(); // _lib.streambuf.virt.pback_ Putback: virtual int_type pbackfail(int_type c = traits::eof()); // _lib.streambuf.virt.put_ Put area: virtual streamsize xsputn(const char_type* s, streamsize n); virtual int_type overflow (int_type c = traits::eof()); }; } 1 The class template basic_streambuf<charT,traits> serves as an abstract base class for deriving various stream buffers whose objects each con- trol two character sequences: --a character input sequence; --a character output sequence. 2 The class streambuf is an instantiation of the template class basic_streambuf specialized by the type char. 3 The class wstreambuf is an instantiation of the template class basic_streambuf specialized by the type wchar_t. 27.5.2.1 basic_streambuf constructors [lib.streambuf.cons] basic_streambuf(); Effects: Constructs an object of class basic_streambuf<charT,traits> and initializes:10) --all its pointer member objects to null pointers, --the getloc() member to a copy the global locale, locale(), at the time of construction. Notes: Once the getloc() member is initialized, results of calling locale member functions, and of members of facets so obtained, can safely be cached until the next time the member imbue is called. 27.5.2.2 basic_streambuf public member [lib.streambuf.members] functions 27.5.2.2.1 Locales [lib.streambuf.locales] locale pubimbue(const locale& loc); Postcondition: loc == getloc(). Effects: Calls imbue(loc). Returns: Previous value of getloc(). locale getloc() const; Returns: If pubimbue() has ever been called, then the last value of loc sup- plied, otherwise the current global locale, locale(), in effect at the time of construction. If called after pubimbue() has been called but before pubimbue has returned (i.e. from within the call of imbue()) then it returns the previous value. 27.5.2.2.2 Buffer management and [lib.streambuf.buffer] positioning basic_streambuf<char_type,traits>* pubsetbuf(char_type* s, streamsize n); _________________________ 10) The default constructor is protected for class basic_streambuf to assure that only objects for classes derived from this class may be constructed. Returns: setbuf(s,n). pos_type pubseekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); Returns: seekoff(off,way,which). pos_type pubseekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); Returns: seekpos(sp,which). int pubsync(); Returns: sync(). 27.5.2.2.3 Get area [lib.streambuf.pub.get] streamsize in_avail(); Returns: If a read position is available, returns egptr() - gptr(). Other- wise returns showmanyc() (_lib.streambuf.virt.get_). int_type snextc(); Effects: Calls sbumpc(). Returns: if that function returns traits::eof(), returns traits::eof(). Oth- erwise, returns sgetc(). int_type sbumpc(); Returns: If the input sequence read position is not available, returns uflow(). Otherwise, returns traits::to_int_type(*gptr()) and incre- ments the next pointer for the input sequence. int_type sgetc(); Returns: If the input sequence read position is not available, returns underflow(). Otherwise, returns traits::to_int_type(*gptr()). streamsize sgetn(char_type* s, streamsize n); Returns: xsgetn(s,n). 27.5.2.2.4 Putback [lib.streambuf.pub.pback] int_type sputbackc(char_type c); Returns: If the input sequence putback position is not available, or if traits::eq(c,gptr()[-1]) is false, returns pback- fail(traits::to_int_type(c)). Otherwise, decrements the next pointer for the input sequence and returns traits::to_int_type(*gptr()). int_type sungetc(); Returns: If the input sequence putback position is not available, returns pbackfail(). Otherwise, decrements the next pointer for the input sequence and returns traits::to_int_type(*gptr()). 27.5.2.2.5 Put area [lib.streambuf.pub.put] int_type sputc(char_type c); Returns: If the output sequence write position is not available, returns overflow(traits::to_int_type(c)). Otherwise, stores c at the next pointer for the output sequence, increments the pointer, and returns traits::to_int_type(c). streamsize sputn(const char_type* s, streamsize n); Returns: xsputn(s,n). 27.5.2.3 basic_streambuf protected [lib.streambuf.protected] member functions 27.5.2.3.1 Get area access [lib.streambuf.get.area] char_type* eback() const; Returns: The beginning pointer for the input sequence. char_type* gptr() const; Returns: The next pointer for the input sequence. char_type* egptr() const; Returns: The end pointer for the input sequence. void gbump(int n); Effects: Advances the next pointer for the input sequence by n. void setg(char_type* gbeg, char_type* gnext, char_type* gend); Postconditions: gbeg == eback(), gnext == gptr(), and gend == egptr(). 27.5.2.3.2 Put area access [lib.streambuf.put.area] char_type* pbase() const; Returns: The beginning pointer for the output sequence. char_type* pptr() const; Returns: The next pointer for the output sequence. char_type* epptr() const; Returns: The end pointer for the output sequence. void pbump(int n); Effects: Advances the next pointer for the output sequence by n. void setp(char_type* pbeg, char_type* pend); Postconditions: pbeg == pbase(), pbeg == pptr(), and pend == epptr(). 27.5.2.4 basic_streambuf virtual [lib.streambuf.virtuals] functions 27.5.2.4.1 Locales [lib.streambuf.virt.locales] void imbue(const locale&) Effects: Change any translations based on locale. Notes: Allows the derived class to be informed of changes in locale at the time they occur. Between invocations of this function a class derived from streambuf can safely cache results of calls to locale functions and to members of facets so obtained. Default behavior: Does nothing. 27.5.2.4.2 Buffer management and [lib.streambuf.virt.buffer] positioning basic_streambuf* setbuf(char_type* s, streamsize n); Effects: Performs an operation that is defined separately for each class derived from basic_streambuf in this clause (_lib.stringbuf.virtu- als_, _lib.filebuf.virtuals_). Default behavior: If gptr() is non-null and gptr()!=egptr() then do nothing. Returns this. pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this clause (_lib.stringbuf.virtuals_, _lib.filebuf.virtuals_). Default behavior: Returns an object of class pos_type that stores an invalid stream position (_lib.iostreams.definitions_). pos_type seekpos(pos_type sp, ios_base::openmode which = in | out); Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this clause (_lib.stringbuf_, _lib.file- buf_). Default behavior: Returns an object of class pos_type that stores an invalid stream position. int sync(); Effects: Synchronizes the controlled sequences with the arrays. That is, if pbase() is non-null the characters between pbase() and pptr() are written to the controlled sequence. The pointers may then be reset as appropriate. Returns: -1 on failure. What constitutes failure is determined by each derived class (_lib.filebuf.virtuals_). Default behavior: Returns zero. 27.5.2.4.3 Get area [lib.streambuf.virt.get] streamsize showmanyc();11) Returns: an estimate of the number of characters available in the sequence, or -1. If it returns a positive value, then successive calls to underflow() will not return traits::eof() until at least that number of characters have been supplied. If showmanyc() returns -1, then calls to underflow() or uflow() will fail.12) Default behavior: Returns zero. Notes: Uses traits::eof(). streamsize xsgetn(char_type* s, streamsize n); _________________________ 11) The morphemes of showmanyc are "es-how-many-see", not "show-man- ic". 12) underflow or uflow might fail by throwing an exception premature- ly. The intention is not only that the calls will not return eof() but that they will return ``immediately.'' Effects: Assigns up to n characters to successive elements of the array whose first element is designated by s. The characters assigned are read from the input sequence as if by repeated calls to sbumpc(). Assigning stops when either n characters have been assigned or a call to sbumpc() would return traits::eof(). Returns: The number of characters assigned.13) Notes: Uses traits::eof(). int_type underflow(); Notes: The public members of basic_streambuf call this virtual function only if gptr() is null or gptr() >= egptr() Returns: traits::to_int_type(c), where c is the first character of the pend- ing sequence, without moving the input sequence position past it. If the pending sequence is null then the function returns traits::eof() to indicate failure. 1 The pending sequence of characters is defined as the concatenation of: a)If gptr() is non- NULL, then the egptr() - gptr() characters start- ing at gptr(), otherwise the empty sequence. b)Some sequence (possibly empty) of characters read from the input sequence. 2 The result character is a)If the pending sequence is non-empty, the first character of the sequence. b)If the pending sequence empty then the next character that would be read from the input sequence. 3 The backup sequence is defined as the concatenation of: a)If eback() is null then empty, b)Otherwise the gptr() - eback() characters beginning at eback(). Effects: The function sets up the gptr() and egptr() satisfying one of: a)If the pending sequence is non-empty, egptr() is non-null and egptr() - gptr() characters starting at gptr() are the characters in _________________________ 13) Classes derived from basic_streambuf can provide more efficient ways to implement xsgetn() and xsputn() by overriding these defini- tions from the base class. the pending sequence b)If the pending sequence is empty, either gptr() is null or gptr() and egptr() are set to the same NULL pointer. 4 If eback() and gptr() are non-null then the function is not con- strained as to their contents, but the ``usual backup condition'' is that either: a)If the backup sequence contains at least gptr() - eback() charac- ters, then the gptr() - eback() characters starting at eback() agree with the last gptr() - eback() characters of the backup sequence. b)Or the n characters starting at gptr() - n agree with the backup sequence (where n is the length of the backup sequence) Default behavior: Returns traits::eof(). int_type uflow(); Requires: The constraints are the same as for underflow(), except that the result character is transferred from the pending sequence to the backup sequence, and the pending sequence may not be empty before the transfer. Default behavior: Calls underflow(). If underflow() returns traits::eof(), returns traits::eof(). Otherwise, returns the value of traits::to_int_type(*gptr()) and increment the value of the next pointer for the input sequence. Returns: traits::eof() to indicate failure. 27.5.2.4.4 Putback [lib.streambuf.virt.pback] int_type pbackfail(int_type c = traits::eof()); Notes: The public functions of basic_streambuf call this virtual function only when gptr() is null, gptr() == eback(), or traits::eq(*gptr(),traits::to_char_type(c)) returns false. Other calls shall also satisfy that constraint. The pending sequence is defined as for underflow(), with the modifi- cations that --If traits::eq_int_type(c,traits::eof()) returns true, then the input sequence is backed up one character before the pending sequence is determined. --If traits::eq_int_type(c,traits::eof()) return false, then c is prepended. Whether the input sequence is backed up or modified in any other way is unspecified. Postcondition: On return, the constraints of gptr(), eback(), and pptr() are the same as for underflow(). Returns: traits::eof() to indicate failure. Failure may occur because the input sequence could not be backed up, or if for some other reason the pointers could not be set consistent with the constraints. pbackfail() is called only when put back has really failed. Returns some value other than traits::eof() to indicate success. Default behavior: Returns traits::eof(). 27.5.2.4.5 Put area [lib.streambuf.virt.put] streamsize xsputn(const char_type* s, streamsize n); Effects: Writes up to n characters to the output sequence as if by repeated calls to sputc(c). The characters written are obtained from succes- sive elements of the array whose first element is designated by s. Writing stops when either n characters have been written or a call to sputc(c) would return traits::eof(). Returns: The number of characters written. int_type overflow(int_type c = traits::eof()); Effects: Consumes some initial subsequence of the characters of the pending sequence. The pending sequence is defined as the concatenation of a)if pbase() is NULL then the empty sequence otherwise, pptr() - pbase() characters beginning at pbase(). b)if traits::eq_int_type(c,traits::eof()) returns true, then the empty sequence otherwise, the sequence consisting of c. Notes: The member functions sputc() and sputn() call this function in case that no room can be found in the put buffer enough to accomodate the argument character sequence. Requires: Every overriding definition of this virtual function shall obey the following constraints: 1)The effect of consuming a character on the associated output sequence is specified14) _________________________ 14) That is, for each class derived from an instance of basic_stream- buf in this clause (_lib.stringbuf_, _lib.filebuf_), a specification of how consuming a character effects the associated output sequence is given. There is no requirement on a program-defined class. 2)Let r be the number of characters in the pending sequence not con- sumed. If r is non-zero then pbase() and pptr() must be set so that: pptr() - pbase() == r and the r characters starting at pbase() are the associated output stream. In case r is zero (all charac- ters of the pending sequence have been consumed) then either pbase() is set to NULL, or pbase() and pptr() are both set to the same NULL value. 3)The function may fail if either appending some character to the associated output stream fails or if it is unable to establish pbase() and pptr() according to the above rules. Returns: traits::eof() or throws an exception if the function fails. Otherwise, returns some value other than traits::eof() to indicate success.15) Default behavior: Returns traits::eof(). 27.6 Formatting and manipulators [lib.iostream.format] Header <istream> synopsis namespace std { template <class charT, class traits = char_traits<charT> > class basic_istream; typedef basic_istream<char> istream; typedef basic_istream<wchar_t> wistream; template <class charT, class traits> basic_istream<charT,traits>& ws(basic_istream<charT,traits>& is); } Header <ostream> synopsis namespace std { template <class charT, class traits = char_traits<charT> > class basic_ostream; typedef basic_ostream<char> ostream; typedef basic_ostream<wchar_t> wostream; template <class charT, class traits> basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os); template <class charT, class traits> basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os); template <class charT, class traits> basic_ostream<charT,traits>& flush(basic_ostream<charT,traits>& os); } Header <iomanip> synopsis _________________________ 15) Typically, overflow returns c to indicate success, except when traits::eq_int_type(c,traits::eof()) returns true, in which case it returns traits::not_eof(c). namespace std { // Types T1, T2, ... are unspecified implementation types T1 resetiosflags(ios_base::fmtflags mask); T2 setiosflags (ios_base::fmtflags mask); T3 setbase(int base); template<charT> T4 setfill(charT c); T5 setprecision(int n); T6 setw(int n); } 27.6.1 Input streams [lib.input.streams] 1 The header <istream> defines two types and a function signature that control input from a stream buffer. 27.6.1.1 Template class basic_istream [lib.istream] namespace std { template <class charT, class traits = char_traits<charT> > class basic_istream : virtual public basic_ios<charT,traits> { public: // Types (inherited from basic_ios (_lib.ios_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.istream.cons_ Constructor/destructor: explicit basic_istream(basic_streambuf<charT,traits>* sb); virtual ~basic_istream(); // _lib.istream::sentry_ Prefix/suffix: class sentry; // _lib.istream.formatted_ Formatted input: basic_istream<charT,traits>& operator>> (basic_istream<charT,traits>& (*pf)(basic_istream<charT,traits>&)) basic_istream<charT,traits>& operator>> (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&)) basic_istream<charT,traits>& operator>> (ios_base& (*pf)(ios_base&)) basic_istream<charT,traits>& operator>>(bool& n); basic_istream<charT,traits>& operator>>(short& n); basic_istream<charT,traits>& operator>>(unsigned short& n); basic_istream<charT,traits>& operator>>(int& n); basic_istream<charT,traits>& operator>>(unsigned int& n); basic_istream<charT,traits>& operator>>(long& n); basic_istream<charT,traits>& operator>>(unsigned long& n); basic_istream<charT,traits>& operator>>(float& f); basic_istream<charT,traits>& operator>>(double& f); basic_istream<charT,traits>& operator>>(long double& f); basic_istream<charT,traits>& operator>>(void*& p); basic_istream<charT,traits>& operator>> (basic_streambuf<char_type,traits>* sb); // _lib.istream.unformatted_ Unformatted input: streamsize gcount() const; int_type get(); basic_istream<charT,traits>& get(char_type& c); basic_istream<charT,traits>& get(char_type* s, streamsize n); basic_istream<charT,traits>& get(char_type* s, streamsize n, char_type delim); basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb); basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb, char_type delim); basic_istream<charT,traits>& getline(char_type* s, streamsize n); basic_istream<charT,traits>& getline(char_type* s, streamsize n, char_type delim); basic_istream<charT,traits>& ignore (streamsize n = 1, int_type delim = traits::eof()); int_type peek(); basic_istream<charT,traits>& read (char_type* s, streamsize n); streamsize readsome(char_type* s, streamsize n); basic_istream<charT,traits>& putback(char_type c); basic_istream<charT,traits>& unget(); int sync(); pos_type tellg(); basic_istream<charT,traits>& seekg(pos_type); basic_istream<charT,traits>& seekg(off_type, ios_base::seekdir); }; // _lib.istream::extractors_ character extraction templates: template<class charT, class traits> basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>&, charT&); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>&, unsigned char&); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>&, signed char&); template<class charT, class traits> basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>&, charT*); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>&, unsigned char*); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>&, signed char*); } 1 The class basic_istream defines a number of member function signatures that assist in reading and interpreting input from sequences con- trolled by a stream buffer. 2 Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc(). They may use other public members of istream. 3 If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits::eof(), then the input function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may throw ios_base::fail- ure (_lib.iostate.flags_), before returning. 4 If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in error state. If badbit is on in exception(), the input function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication. 27.6.1.1.1 basic_istream constructors [lib.istream.cons] explicit basic_istream(basic_streambuf<charT,traits>* sb); Effects: Constructs an object of class basic_istream, assigning initial val- ues to the base class by calling basic_ios::init(sb) (_lib.basic.ios.cons_). Postcondition: gcount() == 0 virtual ~basic_istream(); Effects: Destroys an object of class basic_istream. Notes: Does not perform any operations of rdbuf(). 27.6.1.1.2 Class basic_istream::sentry [lib.istream::sentry] namespace std { template <class charT,class traits = char_traits<charT> > class basic_istream<charT,traits>::sentry { typedef traits traits_type; bool ok_; // exposition only public: explicit sentry(basic_istream<charT,traits>& is, bool noskipws = false); ~sentry(); operator bool() { return ok_; } const; private: sentry(const sentry&); // not defined sentry& operator=(const sentry&); // not defined }; } 1 The class sentry defines a class that is responsible for doing excep- tion safe prefix and suffix operations. explicit sentry(basic_istream<charT,traits>& is, bool noskipws = false); Effects: If is.good() is true, prepares for formatted or unformatted input. First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any asso- ciated external C stream. Except that this call can be suppressed if the put area of is.tie() is empty. Further an implementation is allowed to defer the call to flush until a call of is->rdbuf()->underflow occurs. If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely16) If noskipws is zero and is.flags() & ios_base::skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character. Notes: The constructor explicit sentry(basic_istream<charT,traits>& is, bool noskipws = false) uses the currently imbued locale in is , to determine whether the next input character is whitespace or not. To decide if the character c is a whitespace character, the con- structor performs ``as if'' it executes the following code fragment: const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc()); if (ctype.is(ctype.space,c)!=0) // c is a whitespace character. If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_))17) 2 [Example: A typical implementation of the sentry constructor might include code such as: _________________________ 16) This will be possible only in functions that are part of the li- brary. The semantics of the constructor used in user code is as spec- ified. 17) The sentry constructor and destructor can also perform additional implementation-dependent operations. template <class charT, class traits = char_traits<charT> > basic_istream<charT,traits>::sentry( basic_istream<charT,traits>& is, bool noskipws = false) { ... int_type c; typedef ctype<charT> ctype_type; const ctype_type& ctype = use_facet<ctype_type>(is.getloc()); while ((c = is.rdbuf()->snextc()) != traits::eof()) { if (ctype.is(ctype.space,c)==0) { is.rdbuf()->sputbackc (c); break; } } ... } --end example] ~sentry(); Effects: None. operator bool(); Effects: Returns ok_. 27.6.1.2 Formatted input functions [lib.istream.formatted] 27.6.1.2.1 Common requirements [lib.istream.formatted.reqmts] 1 Each formatted input function begins execution by constructing an object of class sentry with the noskipws (second) argument false. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. If an exception is thrown during input then ios::badbit is turned on18) in *this's error state. If (exception()&badbit)!= 0 then the exception is rethrown In any case, the formatted input function destructs the sentry object. If no exception has been thrown it returns *this 27.6.1.2.2 Arithmetic [lib.istream.formatted.arithmetic] Extractors _________________________ 18) This is done without causing an ios::failure to be thrown. operator>>(short& val); operator>>(unsigned short& val); operator>>(int& val); operator>>(unsigned int& val); operator>>(long& val); operator>>(unsigned long& val); operator>>(float& val); operator>>(double& val); operator>>(long double& val); operator>>(bool& val); operator>>(void*& val); As in the case of the inserters, these extractors depend on the locale's num_get<> (_lib.locale.num.get_) object to perform parsing the input stream data. The conversion occurs as if performed by the following code fragment: typedef num_get< charT,istreambuf_iterator<charT,traits> > numget; iostate err = 0; use_facet< numget >(loc).get(*this, 0, *this, err, val); setstate(err); In the above fragment, loc stands for the private member of the basic_ios class. [Note: The first argument provides an object of the istream_iterator class which is an iterator pointed to an input stream. It bypasses istreams and uses streambufs directly. --end note] Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream. 27.6.1.2.3 basic_istream::operator>> [lib.istream::extractors] basic_istream<charT,traits>& operator>> (basic_istream<charT,traits>& (*pf)(basic_istream<charT,traits>&)) Returns: pf(*this).19) basic_istream<charT,traits>& operator>> (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&)); Effects: Calls pf(*this). Returns: *this. basic_istream<charT,traits>& operator>> (ios_base& (*pf)(ios_base&)); _________________________ 19) See, for example, the function signature ws(basic_istream&) (_lib.istream.manip_). Effects: Calls pf(*this).20) Returns: *this. template<class charT, class traits> basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>& in, charT* s); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in, unsigned char* s); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in, signed char* s); Effects: Behaves like a formatted input member (as described in _lib.istream.formatted.reqmts_) of in. After a sentry object is constructed, operator>> extracts characters and stores them into successive locations of an array whose first element is designated by s. If width() is greater than zero, n is width(). Otherwise n is the the number of elements of the largest array of char_type that can store a terminating eos. n is the maximum number of characters stored. 1 Characters are extracted and stored until any of the following occurs: --n-1 characters are stored; --end of file occurs on the input sequence; --ct.is(ct.space,c) is true for the next available input character c, where ct is use_facet<ctype<charT> >(in.getloc()). --A null byte ( charT()) in the next position, which may be the first position if no characters were extracted. operator>> then calls width(0). 2 If the function extracted no characters, it calls setstate(failbit), which may throw ios_base::failure (_lib.iostate.flags_). Returns: in. _________________________ 20) See, for example, the function signature dec(ios_base&) (_lib.basefield.manip_). template<class charT, class traits> basic_istream<charT,traits>& operator>>(basic_istream<charT,traits>& in, charT& c); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in, unsigned char& c); template<class traits> basic_istream<char,traits>& operator>>(basic_istream<char,traits>& in, signed char& c); Effects: Behaves like a formatted input member (as described in _lib.istream.formatted.reqmts_) of in. After a sentry object is constructed a character is extracted from in, if one is available, and stored in c. Otherwise, the function calls in.setstate(fail- bit). Returns: in. basic_istream<charT,traits>& operator>> (basic_streambuf<charT,traits>* sb); Effects: If sb is null, calls setstate(failbit), which may throw ios_base::failure (_lib.iostate.flags_). Extracts characters from *this and inserts them in the output sequence controlled by sb. Characters are extracted and inserted until any of the following occurs: --end-of-file occurs on the input sequence; --inserting in the output sequence fails (in which case the character to be inserted is not extracted); --an exception occurs (in which case the exception is caught). If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (_lib.iostate.flags_). If failure was due to catching an exception thrown while extracting characters from sb and failbit is on in exceptions() (_lib.iostate.flags_), then the caught exception is rethrown. Returns: *this. 27.6.1.3 Unformatted input functions [lib.istream.unformatted] 1 Each unformatted input function begins execution by constructing an object of class sentry with the default argument noskipws (second) argument true. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. If an exception is thrown during input then ios::badbit is turned on21) in *this's error state. If (exception()&badbit)!= 0 then _________________________ the exception is rethrown It also counts the number of characters extracted. If no exception has been thrown it ends by storing the count in a member object and returning the value specified. In any event the sentry object is destroyed before leaving the unformatted input function. streamsize gcount() const; Returns: The number of characters extracted by the last unformatted input member function called for the object. int_type get(); Effects: Extracts a character c, if one is available. Otherwise, the func- tion calls setstate(failbit), which may throw ios_base::failure (_lib.iostate.flags_), Returns: c if available, otherwise traits::eof(). basic_istream<charT,traits>& get(char_type& c); Effects: Extracts a character, if one is available, and assigns it to c.22) Otherwise, the function calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. basic_istream<charT,traits>& get(char_type* s, streamsize n, char_type delim ); Effects: Extracts characters and stores them into successive locations of an array whose first element is designated by s.23) Characters are extracted and stored until any of the following occurs: --n - 1 characters are stored; --end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit)); _________________________ 21) This is done without causing an ios::failure to be thrown. 22) Note that this function is not overloaded on types signed charand unsigned char. 23) Note that this function is not overloaded on types signed char and unsigned char. --c == delim for the next available input character c (in which case c is not extracted). 2 If the function stores no characters, it calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). In any case, it then stores a null character into the next successive loca- tion of the array. Returns: *this. basic_istream<charT,traits>& get(char_type* s, streamsize n) Effects: Calls get(s,n,widen('\n')) Returns: Value returned by the call. basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb, char_type delim ); Effects: Extracts characters and inserts them in the output sequence con- trolled by sb. Characters are extracted and inserted until any of the following occurs: --end-of-file occurs on the input sequence; --inserting in the output sequence fails (in which case the character to be inserted is not extracted); --c == delim for the next available input character c (in which case c is not extracted); --an exception occurs (in which case, the exception is caught but not rethrown). 3 If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure (_lib.iostate.flags_). Returns: *this. basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb); Effects: Calls get(s,n,widen('\n')) Returns: Value returned by the call. basic_istream<charT,traits>& getline(char_type* s, streamsize n, char_type delim); Effects: Extracts characters and stores them into successive locations of an array whose first element is designated by s.24) Characters are extracted and stored until one of the following occurs: 1)end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit)); 2)c == delim for the next available input character c (in which case the input character is extracted but not stored);25) 3)n - 1 characters are stored (in which case the function calls set- state(failbit)). 4 These conditions are tested in the order shown.26) 5 If the function extracts no characters, it calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)).27) 6 In any case, it then stores a null character (using charT()) into the next successive location of the array. Returns: *this. 7 [Example: _________________________ 24) Note that this function is not overloaded on types signed char and unsigned char. 25) Since the final input character is ``extracted,'' it is counted in the gcount(), even though it is not stored. 26) This allows an input line which exactly fills the buffer, without setting failbit. This is different behavior than the historical AT&T implementation. 27) This implies an empty input line will not cause failbit to be set. #include <iostream> int main() { using namespace std; const int line_buffer_size = 100; char buffer[line_buffer_size]; int line_number = 0; while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount()) { int count = cin.gcount(); if (cin.eof()) cout << "Partial final line"; // cin.fail() is false else if (cin.fail()) { cout << "Partial long line"; cin.clear(cin.rdstate() & ~ios::failbit); } else { count--; // Don't include newline in count cout << "Line " << ++line_number; } cout << " (" << count << " chars): " << buffer << endl; } } --end example] basic_istream<charT,traits>& getline(char_type* s, streamsize n); Returns: getline(s,n,widen('\n')) basic_istream<charT,traits>& ignore(int n = 1, int_type delim = traits::eof()); Effects: Extracts characters and discards them. Characters are extracted until any of the following occurs: --if n != numeric_limits<int>::max() (_lib.limits_), n characters are extracted --end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_base::failure (_lib.iostate.flags_)); --c == delim for the next available input character c (in which case c is extracted). Notes: The last condition will never occur if delim == traits::eof(). Returns: *this. int_type peek(); Returns: traits::eof() if good() is false. Otherwise, returns rdbuf()->sgetc(). basic_istream<charT,traits>& read(char_type* s, streamsize n); Effects: If !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into succes- sive locations of an array whose first element is designated by s.28) Characters are extracted and stored until either of the fol- lowing occurs: --n characters are stored; --end-of-file occurs on the input sequence (in which case the function calls setstate(failbit|eofbit), which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. streamsize readsome(char_type* s, streamsize n); Effects: If !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into succes- sive locations of an array whose first element is designated by s. If rdbuf()->in_avail() == -1, calls setstate(eofbit) (which may throw ios_base::failure (_lib.iostate.flags_)), and extracts no characters; --If rdbuf()->in_avail() == 0, extracts no characters --If rdbuf()->in_avail() > 0, extracts min(rdbuf()->in_avail(),n)). Returns: The number of characters extracted. basic_istream<charT,traits>& putback(char_type c); Effects: If !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf->sputbackc(). If rdbuf() is null, or if sputback() returns traits::eof(), calls _________________________ 28) Note that this function is not overloaded on types signed char and unsigned char. setstate(badbit) (which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. basic_istream<charT,traits>& unget(); Effects: If !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf()->sungetc(). If rdbuf() is null, or if sungetc() returns traits::eof(), calls set- state(badbit) (which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. int sync(); Effects: If rdbuf() is a null pointer, returns -1 . Otherwise, calls rdbuf()->pubsync() and, if that function returns -1 calls set- state(badbit) (which may throw ios_base::failure (_lib.iostate.flags_), and returns traits::eof(). Otherwise, returns zero. pos_type tellg(); Returns: if fail() != false, returns pos_type(-1) to indicate failure. Oth- erwise, returns rdbuf()->pubseekoff(0, cur, in). basic_istream<charT,traits>& seekg(pos_type pos); Effects: If fail() != true, executes rdbuf()->pubseekpos(pos). Returns: *this. basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir); Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir). Returns: *this. 27.6.1.4 Standard basic_istream manipulators [lib.istream.manip] namespace std { template <class charT, class traits> basic_istream<charT,traits>& ws(basic_istream<charT,traits>& is); } Effects: Extracts characters as long as the next available character c is whitespace or until there are no more characters in the sequence. Whitespace characters are distinguished with the same criterion as used by sentry::sentry (_lib.istream::sentry_). If ws stops extracting characters because there are no more available it sets eofbit, but not failbit. Returns: is. 27.6.1.5 Template class basic_iostream [lib.iostreamclass] namespace std { template <class charT, class traits = char_traits<charT> > class basic_iostream : public basic_istream<charT,traits>, public basic_ostream<charT,traits> { public: // constructor/destructor explicit basic_iostream(basic_streambuf<charT,traits>* sb); virtual ~basic_iostream(); }; } 1 The class basic_iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer. 27.6.1.5.1 basic_iostream constructors [lib.iostream.cons] explicit basic_iostream(basic_streambuf<charT,traits>* sb); Effects Constructs an object of class basic_iostream, assigning initial val- ues to the base classes by calling basic_istream<charT,traits>(sb) (_lib.istream_) and basic_ostream<charT,traits>(sb) (_lib.ostream_) Postcondition: rdbuf()==sb and gcount()==0. 27.6.1.5.2 basic_iostream destructor [lib.iostream.dest] virtual ~basic_iostream(); Effects: Destroys an object of class basic_iostream. Notes: Does not perform any operations on rdbuf(). 27.6.2 Output streams [lib.output.streams] 1 The header <ostream> defines a type and several function signatures that control output to a stream buffer. 27.6.2.1 Template class basic_ostream [lib.ostream] namespace std { template <class charT, class traits = char_traits<charT> > class basic_ostream : virtual public basic_ios<charT,traits> { public: // Types (inherited from basic_ios (_lib.ios_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.ostream.cons_ Constructor/destructor: explicit basic_ostream(basic_streambuf<char_type,traits>* sb); virtual ~basic_ostream(); // _lib.ostream::sentry_ Prefix/suffix: class sentry; // _lib.ostream.formatted_ Formatted output: basic_ostream<charT,traits>& operator<< (basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&)); basic_ostream<charT,traits>& operator<< (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&)); basic_ostream<charT,traits>& operator<< (ios_base& (*pf)(ios_base&)); basic_ostream<charT,traits>& operator<<(bool n); basic_ostream<charT,traits>& operator<<(short n); basic_ostream<charT,traits>& operator<<(unsigned short n); basic_ostream<charT,traits>& operator<<(int n); basic_ostream<charT,traits>& operator<<(unsigned int n); basic_ostream<charT,traits>& operator<<(long n); basic_ostream<charT,traits>& operator<<(unsigned long n); basic_ostream<charT,traits>& operator<<(float f); basic_ostream<charT,traits>& operator<<(double f); basic_ostream<charT,traits>& operator<<(long double f); basic_ostream<charT,traits>& operator<<(const void* p); basic_ostream<charT,traits>& operator<< (basic_streambuf<char_type,traits>* sb); // _lib.ostream.unformatted_ Unformatted output: basic_ostream<charT,traits>& put(char_type c); basic_ostream<charT,traits>& write(const char_type* s, streamsize n); basic_ostream<charT,traits>& flush(); // _lib.ostream.seeks_ seeks: pos_type tellp(); basic_ostream<charT,traits>& seekp(pos_type); basic_ostream<charT,traits>& seekp(off_type, ios_base::seekdir); }; // _lib.ostream.inserters.character_ character inserters template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&, charT); template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&, char); // specialization template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, char); // signed and unsigned template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, signed char); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, unsigned char) template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&, const charT*); template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>&, const char*); // partial specializationss template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, const char*); // signed and unsigned template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, const signed char*); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>&, const unsigned char*); } 1 The class basic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences con- trolled by a stream buffer. 2 Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) out- put characters by actions equivalent to calling rdbuf().sputc(int_type). They may use other public members of basic_ostream except that they do not invoke any virtual members of rdbuf() except overflow(). 3 If one of these called functions throws an exception, then unless explicitly noted otherwise the output function set badbit in error state. If badbit is on in exception(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and treat as an error. 27.6.2.2 basic_ostream constructors [lib.ostream.cons] explicit basic_ostream(basic_streambuf<charT,traits>* sb); Effects: Constructs an object of class basic_ostream, assigning initial val- ues to the base class by calling basic_ios<charT,traits>::init(sb) (_lib.basic.ios.cons_). Postcondition: rdbuf() == sb. virtual ~basic_ostream(); Effects: Destroys an object of class basic_ostream. Notes: Does not perform any operations on rdbuf(). 27.6.2.3 Class basic_ostream::sentry [lib.ostream::sentry] namespace std { template <class charT,class traits = char_traits<charT> > class basic_ostream<charT,traits>::sentry { bool ok_; // exposition only public: explicit sentry(basic_ostream<charT,traits>& os); ~sentry(); operator bool() const { return ok_; } private sentry(const sentry&); // not defined sentry& operator=(const sentry&); // not defined }; } 1 The class sentry defines a class that is responsible for doing excep- tion safe prefix and suffix operations. explicit sentry(basic_ostream<charT,traits>& os); 2 If os.good() is nonzero, prepares for formatted or unformatted output. If os.tie() is not a null pointer, calls os.tie()->flush().29) _________________________ 29) The call os.tie()->flush() does not necessarily occur if the func- 3 If, after any preparation is completed, os.good() is true, ok_ == true otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_))30) ~sentry(); 4 If ((os.flags() & ios_base::unitbuf) && !uncaught_exception()) is true, calls os.flush(). operator bool(); Effects: Returns ok_. 27.6.2.4 basic_ostream seek members [lib.ostream.seeks] pos_type tellp(); Returns: if fail() != false, returns pos_type(-1) to indicate failure. Oth- erwise, returns rdbuf()->pubseekoff(0, cur, out). basic_ostream<charT,traits>& seekp(pos_type& pos); Effects: If fail() != true, executes rdbuf()->pubseekpos(pos). Returns: *this. basic_ostream<charT,traits>& seekp(off_type& off, ios_base::seekdir dir); Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir). Returns: *this. 27.6.2.5 Formatted output functions [lib.ostream.formatted] _________________________ tion can determine that no synchronization is necessary. 30) The sentry constructor and destructor can also perform additional implementation-dependent operations. 27.6.2.5.1 Common requirements [lib.ostream.formatted.reqmts] 1 Each formatted output function begins execution by constructing an object of class sentry. If this object returns true when converted to a value of type bool, the function endeavors to generate the requested output. If the generation fails, then the formatted output function does setstate(ios::failbit), which might throw an exception. If an exception is thrown during output, then ios::badbit is turned on31) in *this's error state. If (exception()&badbit) != 0 then the exception is rethrown. Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function. If no exception is thrown, the result of the formattted output function is *this. 2 The descriptions of the individual formatted output operations describe how they perform output and do not mention the sentry object. 27.6.2.5.2 Arithmetic [lib.ostream.inserters.arithmetic] Inserters operator<<(bool val); operator<<(short val); operator<<(unsigned short val); operator<<(int val); operator<<(unsigned int val); operator<<(long val); operator<<(unsigned long val); operator<<(float val); operator<<(double val); operator<<(long double val); operator<<(const void* val); Effects: 1 The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing. These inserter functions refers the imbued locale value to utilize these numeric formatting functionality. The formatting conversion occurs as if it performed the following code fragment: bool failed = use_facet< num_put<charT,ostreambuf_iterator<charT,traits> > >(getloc()). put(*this, *this, fill(), val). failed(); The first argument provides an object of the ostreambuf_iterator<> class which is an iterator for class basic_ostream<>. It bypasses ostreams and uses streambufs directly. Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream. The second parame- ter is a reference to the base subobject of type ios_base. It pro- vides formatting specifications such as field width, and a locale from _________________________ 31) without causing an ios::failure to be thrown. which to obtain other facets. If failed is true then does set- state(badbit), which may throw an exception, and returns. Returns: *this. 27.6.2.5.3 basic_ostream::operator<< [lib.ostream.inserters] basic_ostream<charT,traits>& operator<< (basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&)) Returns: pf(*this).32) basic_ostream<charT,traits>& operator<< (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&)) Effects: Calls pf(*this). Returns: *this.33) basic_ostream<charT,traits>& operator<< (ios_base& (*pf)(ios_base&)) Effects: Calls pf(*this). Returns: *this. basic_ostream<charT,traits>& operator<< (basic_streambuf<charT,traits>* sb); Effects: If sb is null calls setstate(badbit) (which may throw ios_base::failure). 1 Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs: --end-of-file occurs on the input sequence; --inserting in the output sequence fails (in which case the character to be inserted is not extracted); _________________________ 32) See, for example, the function signature endl(basic_ostream&) (_lib.ostream.manip_) . 33) See, for example, the function signature dec(ios_base&) (_lib.basefield.manip_). --an exception occurs while getting a character from sb. 2 If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). If an exception was thrown while extracting a character, the function set failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown. Returns: *this. 27.6.2.5.4 Character inserter [lib.ostream.inserters.character] template functions template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out, charT c); template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out, char c); // specialization template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, char c); // signed and unsigned template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, signed char c); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, unsigned char c); Effects: Behaves like an formatted inserter (as described in _lib.ostream.formatted.reqmts_) of out. After a sentry object is constructed insert characters. In case c has type char and the character type of the stream is not char, then the character to be inserted is out.widen(c); otherwise the character is c34) Padding is determined as described in _lib.facet.num.put.virtuals_. width(0) is called. The insertion character and any required padding are inserted into out. Returns: out _________________________ 34) In case the insertion is into a char stream, widen(c) will usually be c. template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out, const charT* s); template<class charT, class traits> basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out, const char* s); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, const char* s); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, const signed char* s); template<class traits> basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out, const unsigned char* s); Requires: s is non-null. Effects: Behaves like an formatted inserter (as described in _lib.ostream.formatted.reqmts_) of out. After a sentry object is constructed insert characters. The number of characters starting at s to be inserted is traits::length(s). Padding is determined as described in _lib.facet.num.put.virtuals_. The traits::length(s) characters starting at s are widened using out.widen (_lib.basic.ios.members_). The widened characters and any required padding are inserted into out. Calls width(0). Returns: out 27.6.2.6 Unformatted output functions [lib.ostream.unformatted] 1 Each formatted output function begins execution by constructing an object of class sentry. If this object returns true, while converting to a value of type bool, the function endeavors to generate the requested output. In any case, the unformatted output function ends by destroying the sentry object, then returning the value specified for the formatted output function. basic_ostream<charT,traits>& put(char_type c); Effects: Inserts the character c, if possible.35) 2 Otherwise, calls setstate(badbit) (which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. _________________________ 35) Note that this function is not overloaded on types signed char and unsigned char. basic_ostream& write(const char_type* s, streamsize n); Effects: Obtains characters to insert from successive locations of an array whose first element is designated by s.36) Characters are inserted until either of the following occurs: --n characters are inserted; --inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. basic_ostream& flush(); 3 If rdbuf() is not a null pointer, calls rdbuf()->pubsync(). If that function returns -1 calls setstate(badbit) (which may throw ios_base::failure (_lib.iostate.flags_)). Returns: *this. 27.6.2.7 Standard basic_ostream manipulators [lib.ostream.manip] namespace std { template <class charT, class traits> basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os); } Effects: Calls os.put(os.widen('\n') ), then os.flush(). Returns: os.37) namespace std { template <class charT, class traits> basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os); } _________________________ 36) Note that this function is not overloaded on types signed char and unsigned char. 37) The effect of executing cout << endl is to insert a newline char- acter in the output sequence controlled by cout, then synchronize it with any external file with which it might be associated. Effects: Inserts a null character into the output sequence: calls os.put(charT()). Returns: os. namespace std { template <class charT, class traits> basic_ostream<charT,traits>& flush(basic_ostream<charT,traits>& os); } Effects: Calls os.flush(). Returns: os. 27.6.3 Standard manipulators [lib.std.manip] 1 The header <iomanip> defines a type and several related functions that use this type to provide extractors and inserters that alter informa- tion maintained by class ios_base and its derived classes. 2 The type designated smanip in each of the following function descrip- tions is implementation-specified and may be different for each func- tion. smanip resetiosflags(ios_base::fmtflags mask); Returns: An object s of implementation specified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, and if in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as:38) ios_base& f(ios_base& str, ios_base::fmtflags mask) { // reset specified flags str.setf(ios_base::fmtflags(0), mask); return str; } The expression out<<s has type ostream& and value out. The expres- sion in>>s has type istream& and value in. _________________________ 38) The expression cin >> resetiosflags(ios_base::skipws) clears ios_base::skipws in the format flags stored in the istream object cin (the same as cin >> noskipws), and the expression cout << resetios- flags(ios_base::showbase) clears ios_base::showbase in the format flags stored in the ostream object cout (the same as cout << noshow- base). smanip setiosflags(ios_base::fmtflags mask); Returns: An object s of implementation specified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& f(ios_base& str, ios_base::fmtflags mask) { // set specified flags str.setf(mask); return str; } The expression out<<s has type ostream& and value out. The expres- sion in>>s has type istream& and value in. smanip setbase(int base); Returns: An object s of implementation specified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& f(ios_base& str, int base) { // set basefield str.setf(n == 8 ? ios_base::oct : n == 10 ? ios_base::dec : n == 16 ? ios_base::hex : ios_base::fmtflags(0), ios_base::basefield); return str; } The expression out<<s has type ostream& and value out. The expres- sion in>>s has type istream& and value in. smanip setfill(char_type c); Returns: An object s of implementation specified type such that if out is (or is derived from) basic_ostream<charT,traits> and c has type charT then the expression out<<s behaves as if f(s) were called, where f can be defined as: template<class charT, class traits> basic_ios<charT,traits>& f(basic_ios<charT,traits>& str, charT c) { // set fill character str.fill(c); return str; } The expression out<<s has type ostream& and value out. smanip setprecision(int n); Returns: An object s of implementation specified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& f(ios_base& str, int n) { // set precision str.precision(n); return str; } The expression out<<s has type ostream& and value out. The expres- sion in>>s has type istream& and value in. smanip setw(int n); Returns: An object s of implementation specified type such that if out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& f(ios_base& str, int n) { // set width str.width(n); return str; } The expression out<<s has type ostream& and value out. The expres- sion in>>s has type istream& and value in. 27.7 String-based streams [lib.string.streams] 1 The header <sstream> defines four template classes, and six types, that associate stream buffers with objects of class basic_string, as described in _lib.string.classes_. Header <sstream> synopsis namespace std { template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringbuf; typedef basic_stringbuf<char> stringbuf; typedef basic_stringbuf<wchar_t> wstringbuf; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_istringstream; typedef basic_istringstream<char> istringstream; typedef basic_istringstream<wchar_t> wistringstream; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_ostringstream; typedef basic_ostringstream<char> ostringstream; typedef basic_ostringstream<wchar_t> wostringstream; template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringstream; typedef basic_stringstream<char> stringstream; typedef basic_stringstream<wchar_t> wstringstream; } 27.7.1 Template class basic_stringbuf [lib.stringbuf] namespace std { template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringbuf : public basic_streambuf<charT,traits> { public: // Types (inherited from basic_streambuf (_lib.ios_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.stringbuf.cons_ Constructors: explicit basic_stringbuf(ios_base::openmode which = ios_base::in | ios_base::out); explicit basic_stringbuf(const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::in | ios_base::out); // _lib.stringbuf.members_ Get and set: basic_string<charT,traits,Allocator> str() const; void str(const basic_string<charT,traits,Allocator>& s); protected: // _lib.stringbuf.virtuals_ Overridden virtual functions: virtual int_type underflow(); virtual int_type pbackfail(int_type c = traits::eof()); virtual int_type overflow (int_type c = traits::eof()); virtual basic_streambuf<charT,traits>* setbuf(charT*, streamsize); virtual pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); virtual pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); private: // ios_base::openmode mode; exposition only }; } 1 The class basic_stringbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters. The sequence can be initialized from, or made available as, an object of class basic_string. 2 For the sake of exposition, the maintained data is presented here as: --ios_base::openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written. 27.7.1.1 basic_stringbuf constructors [lib.stringbuf.cons] explicit basic_stringbuf(ios_base::openmode which = ios_base::in | ios_base::out); Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() (_lib.streambuf.cons_), and initializ- ing mode with which. Notes: The function allocates no array object. explicit basic_stringbuf(const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::in | ios_base::out); Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() (_lib.streambuf.cons_), and initializ- ing mode with which. Then copies the content of str into the basic_stringbuf underlying character sequence and initializes the input and output sequences according to which. If which & ios_base::out is true, initializes the output sequence with the underlying sequence. If which & ios_base::in is true, initializes the input sequence with the underlying sequence. Postconditions: str() == str. 27.7.1.2 Member functions [lib.stringbuf.members] basic_string<charT,traits,Allocator> str() const; Returns: A basic_string object whose content is equal to the basic_stringbuf underlying character sequence. If the buffer is only created in input mode, the underlying character sequence is equal to the input sequence; otherwise, it is equal to the output sequence. In case of an empty underlying character sequence, the function returns basic_string<charT,traits,Allocator>(). void str(const basic_string<charT,traits,Allocator>& s); Effects: If the basic_stringbuf's underlying character sequence is not empty, deallocates it. Then copies the content of s into the basic_string- buf underlying character sequence and initializes the input and out- put sequences according to the mode stored when creating the basic_stringbuf object. If (mode&ios_base::out) is true, then ini- tializes the output sequence with the underlying sequence. If (mode&ios_base::in) is true, then initializes the input sequence with the underlying sequence. Postcondition: str() == s. 27.7.1.3 Overridden virtual functions [lib.stringbuf.virtuals] int_type underflow(); Returns: If the input sequence has a read position available, returns traits::to_int_type(*gptr()). Otherwise, returns traits::eof(). int_type pbackfail(int_type c = traits::eof()); Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways: --If traits::eq_int_type(c,traits::eof()) returns false and if the input sequence has a putback position available, and if traits::eq(to_char_type(c),gptr()[-1]) returns true, assigns gptr() - 1 to gptr(). Returns: c. --If traits::eq_int_type(c,traits::eof()) returns false and if the input sequence has a putback position available, and if mode & ios_base::out is nonzero, assigns c to *--gptr(). Returns: c. --If traits::eq_int_type(c,traits::eof()) returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr(). Returns: traits::not_eof(c). Returns: traits::eof() to indicate failure. Notes: If the function can succeed in more than one of these ways, it is unspecified which way is chosen. int_type overflow(int_type c = traits::eof()); Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways: --If traits::eq_int_type(c,traits::eof()) returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c). Signals success by returning c. --If traits::eq_int_type(c,traits::eof()) returns true, there is no character to append. Signals success by returning a value other than traits::eof(). Notes: The function can alter the number of write positions available as a result of any call. Returns: traits::eof() to indicate failure. 1 Notes: The function can make a write position available only if (mode & ios_base::out) != 0. To make a write position available, the func- tion reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus one additional write position. If (mode & ios_base::in) != 0, the function alters the read end pointer egptr() to point just past the new write position (as does the write end pointer epptr()). pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); +------- BEGIN BOX 3 -------+ Check vs. _lib.filebuf.virtuals_ +------- END BOX 3 -------+ Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 9: Table 9--seekoff positioning +----------------------------------------------------------------------------------+ | Conditions Result | +----------------------------------------------------------------------------------+ |(which & basic_ios::in) != 0 positions the input sequence | +----------------------------------------------------------------------------------+ |(which & basic_ios::out) != 0 positions the output sequence | +----------------------------------------------------------------------------------+ |(which & (basic_ios::in | ba- positions both the input and the output sequences | |sic_ios::out)) == (ba- | |sic_ios::in | ba- | |sic_ios::out)) | |and way == either ba- | |sic_ios::beg or ba- | |sic_ios::end | +----------------------------------------------------------------------------------+ |Otherwise the positioning operation fails. | +----------------------------------------------------------------------------------+ 2 For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer, the positioning operation fails. Other- wise, the function determines newoff as indicated in Table 10: Table 10--newoff values ----------------------------------------------------------- Condition newoff Value ----------------------------------------------------------- way == basic_ios::beg 0 ----------------------------------------------------------- way == basic_ios::cur the next pointer minus the be- ginning pointer (xnext - xbeg). ----------------------------------------------------------- way == basic_ios::end the end pointer minus the be- ginning pointer (xend - xbeg) ----------------------------------------------------------- If (newoff + off) < 0, the positioning operation fails or (xend - xbeg) < (newoff + off) ----------------------------------------------------------- | | | | | | | | | | 3 Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext. Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possi- ble. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the object stores an invalid stream position. pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); Effects: Alters the stream position within the controlled sequences, if pos- sible, to correspond to the stream position stored in sp (as described below). --If (which & basic_ios::in) != 0, positions the input sequence. --If (which & basic_ios::out) != 0, positions the output sequence. --If sp is an invalid stream position, of if the function positions neither sequence, the positioning operation fails. If sp has not been obtained by a previous successful call to one of the position- ing functions( seekoff, seekpos, tellg, tellp ) the effect is unde- fined. Returns: sp to indicate success, or pos_type(off_type(-1)) to indicate fail- ure. basic_streambuf<charT,traits>* setbuf(charT* s, streamsize n); Effects: implementation-defined, except that setbuf(0,0) has no effect. Returns: this. 27.7.2 Template class basic_istringstream [lib.istringstream] namespace std { template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_istringstream : public basic_istream<charT,traits> { public: // Types (inherited from basic_istream (_lib.input.streams_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.istringstream.cons_ Constructors: explicit basic_istringstream(ios_base::openmode which = ios_base::in); explicit basic_istringstream( const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::in); // _lib.istringstream.members_ Members: basic_stringbuf<charT,traits,Allocator>* rdbuf() const; basic_string<charT,traits,Allocator> str() const; void str(const basic_string<charT,traits,Allocator>& s); private: // basic_stringbuf<charT,traits,Allocator> sb; exposition only }; } 1 The class basic_istringstream<charT,traits,Allocator> supports reading objects of class basic_string<charT,traits,Allocator>. It uses a basic_stringbuf<charT,traits,Allocator> object to control the associ- ated storage. For the sake of exposition, the maintained data is pre- sented here as: --sb, the stringbuf object. 27.7.2.1 basic_istringstream [lib.istringstream.cons] constructors explicit basic_istringstream(ios_base::openmode which = ios_base::in); Effects: Constructs an object of class basic_istringstream<charT,traits>, initializing the base class with basic_istream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(which|ios_base::in)) (_lib.stringbuf.cons_). explicit basic_istringstream( const basic_string<charT,traits,allocator>& str, ios_base::openmode which = ios_base::in); Effects: Constructs an object of class basic_istringstream<charT,traits>, initializing the base class with basic_istream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(str, which | ios_base::in)) (_lib.stringbuf.cons_). 27.7.2.2 Member functions [lib.istringstream.members] basic_stringbuf<charT,traits,Allocator>* rdbuf() const; Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb. basic_string<charT,traits,Allocator> str() const; Returns: rdbuf()->str().39) void str(const basic_string<charT,traits,Allocator>& s); Effects: Calls rdbuf()->str(s). 27.7.3 Class basic_ostringstream [lib.ostringstream] namespace std { template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_ostringstream : public basic_ostream<charT,traits> { public: // Types: typedef charT char_type; typedef typename traits::int_type int_type; typedef typename traits::pos_type pos_type; typedef typename traits::off_type off_type; // _lib.ostringstream.cons_ Constructors/destructor: explicit basic_ostringstream(ios_base::openmode which = ios_base::out); explicit basic_ostringstream( const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::out); // _lib.ostringstream.members_ Members: basic_stringbuf<charT,traits,Allocator>* rdbuf() const; basic_string<charT,traits,Allocator> str() const; void str(const basic_string<charT,traits,Allocator>& s); private: // basic_stringbuf<charT,traits,Allocator> sb; exposition only }; } 1 The class basic_ostringstream<charT,traits,Allocator> supports writing objects of class basic_string<charT,traits,Allocator>. It uses a basic_stringbuf object to control the associated storage. For the sake of exposition, the maintained data is presented here as: --sb, the stringbuf object. _________________________ 39) rdbuf() is never NULL because it always returns the private ob- ject. 27.7.3.1 basic_ostringstream [lib.ostringstream.cons] constructors explicit basic_ostringstream(ios_base::openmode which = ios_base::out); Effects: Constructs an object of class basic_ostringstream, initializing the base class with basic_ostream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(which | ios_base::out)) (_lib.stringbuf.cons_). explicit basic_ostringstream( const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::out); Effects: Constructs an object of class basic_ostringstream<charT,traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(str, which | ios_base::out)) (_lib.stringbuf.cons_). 27.7.3.2 Member functions [lib.ostringstream.members] basic_stringbuf<charT,traits,Allocator>* rdbuf() const; Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb. basic_string<charT,traits,Allocator> str() const; Returns: rdbuf()->str().40) void str(const basic_string<charT,traits,Allocator>& s); Effects: Calls rdbuf()->str(s). 27.7.4 Template class basic_stringstream [lib.stringstream] _________________________ 40) rdbuf() is never NULL because it always returns the private ob- ject. namespace std { template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_stringstream : public basic_iostream<charT,traits> { public: // Types typedef charT char_type; typedef typename traits::int_type int_type; typedef typename traits::pos_type pos_type; typedef typename traits::off_type off_type; // constructors/destructors explicit basic_stringstream( ios_base::openmode which = ios_base::out|ios_base::in); explicit basic_stringstream( const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::out|ios_base::in); // Members: basic_stringbuf<charT,traits,Allocator>* rdbuf() const; basic_string<charT,traits,Allocator> str() const; void str(const basic_string<charT,traits,Allocator>& str); private: // basic_stringbuf<charT, traits> sb; exposition only }; 1 The template class basic_stringstream<charT,traits> supports reading and writing from objects of class basic_string<charT,traits,Alloca- tor>. It uses a basic_stringbuf<charT,traits,Allocator> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as --sb, the stringbuf object. 27.7.5 basic_stringstream constructors [lib.stringstream.cons] explicit basic_stringstream( ios_base::openmode which = ios_base::out|iosbase::in); Effects: Constructs an object of class basic_stringstream<charT,traits>, ini- tializing the base class with basic_iostream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(which). explicit basic_stringstream( const basic_string<charT,traits,Allocator>& str, ios_base::openmode which = ios_base::out|iosbase::in); Effects: Constructs an object of class basic_stringstream<charT,traits>, ini- tializing the base class with basic_iostream(&sb) and initializing sb with basic_stringbuf<charT,traits,Allocator>(str,which). 27.7.6 Member functions [lib.stringstream.members] basic_stringbuf<charT,traits,Allocator>* rdbuf() const; Returns: &sb basic_string<charT,traits,Allocator> str() const; Returns: rdbuf()->str().41) void str(const basic_string<charT,traits,Allocator>& str); Effects: Calls rdbuf()->str(str). 27.8 File-based streams [lib.file.streams] 27.8.1 File streams [lib.fstreams] 1 The header <fstream> defines four class templates, and six types, that associate stream buffers with files and assist reading and writing files. Header <fstream> synopsis _________________________ 41) rdbuf() is never NULL because it always returns the private ob- ject. namespace std { template <class charT, class traits = char_traits<charT> > class basic_filebuf; typedef basic_filebuf<char> filebuf; typedef basic_filebuf<wchar_t> wfilebuf; template <class charT, class traits = char_traits<charT> > class basic_ifstream; typedef basic_ifstream<char> ifstream; typedef basic_ifstream<wchar_t> wifstream; template <class charT, class traits = char_traits<charT> > class basic_ofstream; typedef basic_ofstream<char> ofstream; typedef basic_ofstream<wchar_t> wofstream; template <class charT, class traits = char_traits<charT> > class basic_fstream; typedef basic_fstream<char> fstream; typedef basic_fstream<wchar_t> wfstream; } +------- BEGIN BOX 4 -------+ Issue: basic_filebuf<charT,traits> should be specified so that it treats a file as a sequence of charT. Except for filebuf and wfilebuf that implies it treats the file as binary. +------- END BOX 4 -------+ 2 In this subclause, the type name FILE refers to the type FILE defined in <cstdio> (_lib.c.files_).42) --File A File provides an external source/sink stream whose underlaid character type is char (byte).43) --Multibyte character and Files A File provides byte sequences. So the streambuf (or its derived classes) treats a file as the external source/sink byte sequence. In a large character set environment, multibyte character sequences are held in files. In order to pro- vide the contents of a file as wide character sequences, wide-ori- ented filebuf, namely wfilebuf should convert wide character sequences. _________________________ 42) In C FILE must be a typedef. In C++ it may be a typedef or other type name. 43) A File is a sequence of multibyte characters. In order to provide the contents as a wide character sequence, filebuf should convert be- tween wide character sequences and multibyte character sequences. 27.8.1.1 Template class basic_filebuf [lib.filebuf] namespace std { template <class charT, class traits = char_traits<charT> > class basic_filebuf : public basic_streambuf<charT,traits> { public: // Types (inherited from basic_streambuf (_lib.streambuf_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.filebuf.cons_ Constructors/destructor: basic_filebuf(); virtual ~basic_filebuf(); // _lib.filebuf.members_ Members: bool is_open() const; basic_filebuf<charT,traits>* open(const char* s, ios_base::openmode mode); basic_filebuf<charT,traits>* close(); protected: // _lib.filebuf.virtuals_ Overridden virtual functions: virtual streamsize showmanyc(); virtual int_type underflow(); virtual int_type uflow(); virtual int_type pbackfail(int_type c = traits::eof()); virtual int_type overflow (int_type c = traits::eof()); virtual basic_streambuf<charT,traits>* setbuf(char_type* s, streamsize n); virtual pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out); virtual pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out); virtual int sync(); virtual void imbue(const locale& loc); }; } 1 The class basic_filebuf<charT,traits> associates both the input sequence and the output sequence with a file. 2 The restrictions on reading and writing a sequence controlled by an object of class basic_filebuf<charT,traits> are the same as for read- ing and writing with the Standard C library FILEs. 3 In particular: --If the file is not open for reading the input sequence cannot be read. --If the file is not open for writing the output sequence cannot be written. --A joint file position is maintained for both the input sequence and the output sequence. 4 An instance of basic_filebuf behaves as described in _lib.filebuf_ provided traits::pos_type is fpos<traits::state_type>. Otherwise the behavior is undefined. 5 In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a facet, referred to as a_codecvt in following sections, obtained ``as if'' by codecvt<charT,char,typename traits::state_type> a_codecvt = use_facet<codecvt<charT,char,typename traits::state_type> >(getloc()); 27.8.1.2 basic_filebuf constructors [lib.filebuf.cons] basic_filebuf(); Effects: Constructs an object of class basic_filebuf<charT,traits>, initial- izing the base class with basic_streambuf<charT,traits>() (_lib.streambuf.cons_). Postcondition: is_open() == false. virtual ~basic_filebuf(); Effects: Destroys an object of class basic_filebuf<charT,traits>. Calls close(). 27.8.1.3 Member functions [lib.filebuf.members] bool is_open() const; Returns: true if a previous call to open succeeded (returned a non-null value) and there has been no intervening call to close. basic_filebuf<charT,traits>* open( const char* s, ios_base::openmode mode ); Effects: If is_open() != false, returns a null pointer. Otherwise, initial- izes the filebuf as required. It then opens a file, if possible, whose name is the NTBS s (``as if'' by calling ::fopen(s,modstr)). The NTBS modstr is determined from mode & ~ios_base::ate as indi- cated in Table 11: Table 11--File open modes +---------------------------------------------------+ | ios_base Flag combination stdio equivalent | |binary in out trunc app | +---------------------------------------------------+ | + "w" | +---------------------------------------------------+ | + + "a" | +---------------------------------------------------+ | + + "w" | +---------------------------------------------------+ | + "r" | +---------------------------------------------------+ | + + "r+" | +---------------------------------------------------+ | + + + "w+" | +---------------------------------------------------+ | + + "wb" | +---------------------------------------------------+ | + + + "ab" | +---------------------------------------------------+ | + + + "wb" | +---------------------------------------------------+ | + + "rb" | +---------------------------------------------------+ | + + + "r+b" | +---------------------------------------------------+ | + + + + "w+b" | +---------------------------------------------------+ If mode is not some combination of flags shown in the table then the open fails. 1 If the open operation succeeds and (mode & ios_base::ate) != 0, posi- tions the file to the end (``as if'' by calling ::fseek(file,0,SEEK_END)).44) 2 If the repositioning operation fails, calls close() and returns a null pointer to indicate failure. Returns: this if successful, a null pointer otherwise. basic_filebuf<charT,traits>* close(); _________________________ 44) The macro SEEK_END is defined, and the function signatures fopen(const char_type*, const char_type*) and fseek(FILE*, long, int) are declared, in <cstdio> (_lib.c.files_). Effects: If is_open() == false, returns a null pointer. If a put area exists, calls overflow(EOF) to flush characters. If the last vir- tual member function called on *this (between underflow, overflow, seekoff, and seekpos) was overflow then calls a_codecvt.unshift (possibly several times) to determine a termination sequence, inserts those characters and calls overflow(EOF) again. Finally it closes the file (``as if'' by calling ::fclose(file)).45) If any of the calls to overflow or ::fclose fails then close fails Returns: this on success, a null pointer otherwise. Postcondition: is_open() == false. 27.8.1.4 Overridden virtual functions [lib.filebuf.virtuals] streamsize showmanyc(); Effects: Behaves the same as basic_streambuf::showmanyc() (_lib.stream- buf.virtuals_). Notes: An implementation might well provide an overriding definition for this function signature if it can determine that more characters can be read from the input sequence. int_type underflow(); Effects: Behaves according to the description of basic_stream- buf<charT,traits>:: underflow(), with the specialization that a sequence of characters is read from the input sequence ``as if'' by reading from the associated file into an internal buffer ( extern_buf) and then ``as if'' doing char extern_buf[XSIZE]; char* extern_end; charT intern_buf[ISIZE]; charT* intern_end; codecvt_base::result r = a_codecvt.in(st, extern_buf, extern_buf+XSIZE, extern_end, intern_buf, intern_buf+ISIZE, intern_end); This must be done in such a way that the class can recover the posi- tion fpos_t) corresponding to each character between intern_buf and intern_end. If the value of r indicates that a_codecvt.in() ran out of space in intern_buf, retry with a larger intern_buf. _________________________ 45) The function signature fclose(FILE*) is declared, in <cstdio> (_lib.c.files_). int_type uflow(); Effects: Behaves according to the description of basic_stream- buf<charT,traits>:: uflow(), with the specialization that a sequence of characters is read from the input with the same method as used by underflow. int_type pbackfail(int_type c = traits::eof()); Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways: --If traits::eq_int_type(c,traits::eof()) returns false and if the function makes a putback position available and if traits::eq(to_char_type(c),gptr()[-1]) returns true, decrements the next pointer for the input sequence, gptr(). Returns: c. --If traits::eq_int_type(c,traits::eof()) returns false and if the function makes a putback position available, and if the function is permitted to assign to the putback position, decrements the next pointer for the input sequence, and stores c there. Returns: c. --If traits::eq_int_type(c,traits::eof()) returns true and if either the input sequence has a putback position available or the function makes a putback position available, decrements the next pointer for the input sequence, gptr(). Returns: traits::not_eof(c). Returns: traits::eof() to indicate failure. Notes: If is_open() == false, the function always fails. The function does not put back a character directly to the input sequence. If the function can succeed in more than one of these ways, it is unspecified which way is chosen. The function can alter the number of putback positions available as a result of any call. int_type overflow(int_type c = traits::eof()); Effects: Behaves according to the description of basic_stream- buf<charT,traits>::overflow(c), except that the behavior of ``con- suming characters'' is performed by first coverting ``as if'' by: charT* b = pbase(); charT* p = pptr(); charT* end; char xbuf[XSIZE]; char* xbuf_end; codecvt_base::result r = a_codecvt.out(st, b, p, end, xbuf, xbuf+XSIZE, xbuf_end); and then --If r == codecvt_base::error then fail. --If r == codecvt_base::noconv then output characters from b upto (and not including) p. --If r == codecvt_base::partial then output to the file characters from xbuf upto xbuf_end, and repeat using characters from end to p. If output fails, fail (without repeating). --Otherwise output from xbuf to xbuf_end, and fail if output fails. At this point if b != p and b == end ( buf isn't large enough) then increase BSIZE and repeat from the beginning. Returns: traits::not_eof(c) to indicate success, and traits::eof() to indi- cate failure. If is_open() == false, the function always fails. basic_streambuf* setbuf(char_type* s, int n); Effects: If setbuf(0,0) is called on a stream before any I/O has occured on that stream, the stream becomes unbuffered. Otherwise the results are implementation-defined. "Unbuffered" means that pbase() and pptr() always return null and output to the file should appear as soon as possible. pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode = ios_base::in | ios_base::out); Effects: If is_open() == false, the positioning operation fails. Otherwise, if a_codecvt.encoding()>0 repositions the sequence by off*a_codecvt.encoding() positions in file. This is done by some combination of manipulating the put or get area and repositioning of the file (``as if'' by computing distance, the number of characters to be moved in file and calling ::fseek(file,distance*off,whence).46) Otherwise if off==0 _________________________ 46) The macros SEEK_SET, SEEK_CUR, and SEEK_END are defined, and the function signature fseek(FILE*, long, int) is declared, in <cstdio> (_lib.c.files_). repositions within the associated file (``as if'' by calling ::fseek(file,0,whence). Otherwise the positioning operation fails. Notes: The function determines one of three values for the argument whence, of type int, as indicated in Table 12: Table 12--seekoff effects +----------------------------------+ | way Value stdio Equivalent | +----------------------------------+ |basic_ios::beg SEEK_SET | |basic_ios::cur SEEK_CUR | |basic_ios::end SEEK_END | +----------------------------------+ Returns: a newly constructed pos_type object that stores the resultant stream position, if possible. If the positioning operation fails, or if the object cannot represent the resultant stream position, returns an invalid stream position (_lib.fpos_). pos_type seekpos(pos_type sp, ios_base::openmode = ios_base::in | ios_base::out); Alters the file position, if possible, to correspond to the position stored in sp (as described below). --if (which&ios_base::in)!=0, set the file position to sp, then update the input sequence --if (which&ios_base::out)!=0, set the file position to sp, then update the output sequence 1 If sp is an invalid stream position, or if the function positions nei- ther sequence, the positioning operation fails. If sp has not been obtained by a previous successful call to one of the positioning func- tions seekoff or seekpos) on the same file the effects are undefined. Returns: sp on success. Otherwise returns an invalid stream position (_lib.iostreams.definitions_). int sync(); Effects: If a put area exists, calls filebuf::overflow to write the charac- ters to the file. If a get area exists, the effect is implementa- tion-defined. void imbue(const locale& loc); Precondition: If the file is not positioned at its beginning and the encoding of the current locale as determined by a_codecvt.encoding() is state- dependent (_lib.locale.codecvt.virtuals_) then that facet is the same as the corresponding facet of loc. +------- BEGIN BOX 5 -------+ The library WG believes the correct description of the effects of imbue is as follows. Incorporating this however would create a con- flict with the current description of overflow and underflow. The current descriptions defer conversion until a complete put or get area is processed. To properly decscribe imbue, conversions must be described as if they occur a the time of insertion or extraction. Effects Causes characters inserted or extracted after this call to be con- verted according to loc until another call of imbue. +------- END BOX 5 -------+ Effects: Causes characters inserted or extracted after this call to be con- verted according to loc until another call of imbue. Note: This may require reconversion of previously converted characters. This in turn may require the implementation to be able to recon- struct the original contents of the file. 27.8.1.5 Template class basic_ifstream [lib.ifstream] namespace std { template <class charT, class traits = char_traits<charT> > class basic_ifstream : public basic_istream<charT,traits> { public: // Types (inherited from basic_istream (_lib.istream_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.ifstream.cons_ Constructors: basic_ifstream(); explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); // _lib.ifstream.members_ Members: basic_filebuf<charT,traits>* rdbuf() const; bool is_open(); void open(const char* s, openmode mode = in); void close(); private: // basic_filebuf<charT,traits> sb; exposition only }; } 1 The class basic_ifstream<charT,traits> supports reading from named files. It uses a basic_filebuf<charT,traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as: --sb, the filebuf object. 27.8.1.6 basic_ifstream constructors [lib.ifstream.cons] basic_ifstream(); Effects: Constructs an object of class basic_ifstream<charT,traits>, initial- izing the base class with basic_istream(&sb) and initializing sb with basic_filebuf<charT,traits>()) (_lib.istream.cons_, _lib.file- buf.cons_). explicit basic_ifstream(const char* s, openmode mode = in); Effects: Constructs an object of class basic_ifstream, initializing the base class with basic_istream(&sb) and initializing sb with basic_file- buf<charT,traits>()) (_lib.istream.cons_, _lib.filebuf.cons_), then calls rdbuf()->open(s,mode|in).47) If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::fail- ure). 27.8.1.7 Member functions [lib.ifstream.members] basic_filebuf<charT,traits>* rdbuf() const; Returns: (basic_filebuf<charT,traits>*)&sb. bool is_open(); Returns: rdbuf()->is_open().48) void open(const char* s, openmode mode = in); _________________________ 47) rdbuf() is never NULL because it always returns the private ob- ject. 48) rdbuf() is never NULL because it always returns the private ob- ject. Effects: Calls rdbuf()->open(s,mode|in). If that function returns a null pointer , calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). void close(); Effects: Calls rdbuf()->close() and, if that function returns false, calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). 27.8.1.8 Template class basic_ofstream [lib.ofstream] namespace std { template <class charT, class traits = char_traits<charT> > class basic_ofstream : public basic_ostream<charT,traits> { public: // Types (inherited from basic_ostream (_lib.ostream_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // _lib.ofstream.cons_ Constructors: basic_ofstream(); explicit basic_ofstream(const char* s, ios_base::openmode mode = ios_base::out | ios_base::trunc); // _lib.ofstream.members_ Members: basic_filebuf<charT,traits>* rdbuf() const; bool is_open(); void open(const char* s, ios_base::openmode mode = out | trunc); void close(); private: // basic_filebuf<charT,traits> sb; exposition only }; } 1 The class basic_ofstream<charT,traits> supports writing to named files. It uses a basic_filebuf<charT,traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as: --sb, the filebuf object. 27.8.1.9 basic_ofstream constructors [lib.ofstream.cons] basic_ofstream(); Effects: Constructs an object of class basic_ofstream<charT,traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_filebuf<charT,traits>()) (_lib.ostream.cons_, _lib.filebuf.cons_). explicit basic_ofstream(const char* s, openmode mode = out); Effects: Constructs an object of class basic_ofstream<charT,traits>, initial- izing the base class with basic_ostream(&sb) and initializing sb with basic_filebuf<charT,traits>()) (_lib.ostream.cons_, _lib.file- buf.cons_), then calls rdbuf()->open(s, mode|out).49) If that func- tion returns a null pointer, calls setstate(failbit), (which may throw ios_base::failure). 27.8.1.10 Member functions [lib.ofstream.members] basic_filebuf<charT,traits>* rdbuf() const; Returns: (basic_filebuf<charT,traits>*)&sb. bool is_open(); Returns: rdbuf()->is_open(). void open(const char* s, openmode mode = out); Effects: Calls rdbuf()->open(s,mode|out). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). void close(); Effects: Calls rdbuf()->close() and, if that function fails (returns a null pointer), calls setstate(failbit) (which may throw ios_base::failure (_lib.iostate.flags_)). _________________________ 49) rdbuf() is never NULL because it always returns the private file- buf object. 27.8.1.11 Template class basic_fstream [lib.fstream] namespace std { template <class charT, class traits=char_traits<charT> > class basic_fstream : public basic_iostream<charT,traits> { public: // Types (inherited from basic_istream (_lib.istream_)): // typedef charT char_type; // typedef typename traits::int_type int_type; // typedef typename traits::pos_type pos_type; // typedef typename traits::off_type off_type; // typedef traits traits_type; // constructors/destructor basic_fstream(); explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in|ios_base::out); // Members: basic_filebuf<charT,traits>* rdbuf() const; bool is_open(); void open( const char* s, ios_base::openmode mode = ios_base::in|ios_base::out); void close(); private: // basic_filebuf<charT,traits> sb; exposition only }; 1 The template class basic_fstream<charT,traits> supports reading and writing from named files. It uses a basic_filebuf<charT,traits> object to control the associated sequences. For the sake of exposi- tion, the maintained data is presented here as: --sb, the basic_filebuf object. 27.8.1.12 basic_fstream constructors [lib.fstream.cons] basic_fstream(); Effects: Constructs an object of class basic_fstream<charT,traits>, initial- izing the base class with basic_iostream(&sb) and initializing sb with basic_filebuf<charT,traits>(). explicit basic_fstream(const char* s, ios_base::openmode mode); Effects: Constructs an object of class basic_fstream<charT,traits>, initial- izing the base class with basic_iostream(&sb) and initializing sb with basic_filebuf<charT,traits>(). Then calls rdbuf()->open(s,mode). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure). 27.8.1.13 Member functions [lib.fstream.members] basic_filebuf<charT,traits>* rdbuf() const; Returns: &sb bool is_open(); Returns: rdbuf()->is_open(). void open(const char* s, ios_base::openmode mode); Effects: Calls rdbuf()->open(s,mode), If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::fail- ure). (_lib.iostate.flags_) ) void close(); Effects: Calls rdbuf()->close() and, if that function returns false, calls setstate(failbit)(_lib.iostate.flags_) (which may throw ios_base::failure). 27.8.2 C Library files [lib.c.files] 1 Table 13 describes header <cstdio>. Table 13--Header <cstdio> synopsis +-------------------------------------------------------------------------------+ | Type Name(s) | +-------------------------------------------------------------------------------+ |Macros: | |BUFSIZ L_tmpnam SEEK_SET TMP_MAX | |EOF NULL <cstdio> stderr _IOFBF | |FILENAME_MAX SEEK_CUR stdin _IOLBF | |FOPEN_MAX SEEK_END stdout _IONBF | +-------------------------------------------------------------------------------+ |Types: FILE fpos_t size_t <cstdio> | +-------------------------------------------------------------------------------+ |Functions: | |clearerr fgets fscanf gets rewind | |fclose fopen fseek perror scanf tmpnam | |feof fprintf fsetpos printf setbuf ungetc | |ferror fputc ftell putc setvbuf vprintf | |fflush fputs fwrite puts sprintf vfprintf | |fgetc fread getc remove sscanf vsprintf | |fgetpos freopen getchar putchar rename tmpfile | +-------------------------------------------------------------------------------+ SEE ALSO: ISO C subclause 7.9, Amendment 1 subclause 4.6.2.