______________________________________________________________________
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]
+------- BEGIN BOX 1 -------+
Move these to an Annex containing a Glossary of terms
+------- END BOX 1 -------+
1 Additional definitions:
--character In this clause, the term ``character'' means any unit ele
ment which, treated sequentially, can represent text. The term does
not only mean char and wchar_t type objects, but any value which can
be represented by a type which provides the definitions specified in
(_lib.string.char.traits_).
--character container type Character container type is a class or a
type used to represent a character. It is used for one of the tem
plate parameter of the iostream class templates.
--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 Type requirements [lib.iostreams.type.reqmts]
1 There are several types and functions needed for implementing the
iostream class templates. Some of these types and functions depend on
the definition of the character container type. The collection of
these functions describes the behavior which the implementation of the
iostream class templates expects to the character container class.
27.1.2.1 Type CHAR_T [lib.iostreams.char.t]
1 Those C++ programs that provide a character container type as the tem
plate parameter have to provide all of these functions as well as the
container class itself. The collection of these functions can be
regarded as the collection of the common definitions for the implemen
tation of the character container class.
2 No special definition/declaration is provided here. The base class
(or struct), string_char_traits provides the definitions common
between the string class templates and the iostream class templates.
3 Convertible to type INT_T.
27.1.2.2 Type INT_T [lib.iostreams.int.t]
1 Another character container type which can also hold an end-of-file
value. It is used as the return type of some of the iostream class
member functions. If CHAR_T is either char or wchar_t, INT_T shall be
int or wint_t, respectively.
27.1.2.3 Type OFF_T [lib.iostreams.off.t]
1 A type that can represent offsets to positional information.1) It is
used to represent:
--a signed displacement, measured in characters, from a specified
position within a sequence.
--an absolute position within a sequence.
2 The value OFF_T(-1) can be used as an error indicator.
3 The effect of passing to any function defined in this clause an OFF_T
value not obtained from a function defined in this clause (for exam
ple, assigned an arbitrary integer), is undefined, except where other
wise noted.
4 Convertible to type POS_T.2) But no validity of the resulting POS_T
value is ensured, whether or not the OFF_T value is valid.
27.1.2.4 Type POS_T [lib.iostreams.pos.t]
1 An implementation-defined type for seek operations which describes an
object that can store all the information necessary to reposition to
the position.
2 The type POS_T describes an object that can store all the information
necessary to restore an arbitrary sequence to a previous stream
_________________________
1) It is usually a synonym for one if the signed basic integral types
whose representation at least as many bits as type long.
2) An implementation may use the same type for both OFF_T and POS_T.
position and conversion state.3)
3 With a stream buffer for a repositional stream (but not an arbitrary-
positional stream), a C++ program can either obtain the current posi
tion of the stream buffer or specify the previous position previously
obtained
4 A class or built-in type P satisfies the requirements of a position
type, and a class or built-in type O satisfies the requirements of an
offset type if the following expressions are valid, as shown in Table
2.
5 In the following table,
--P refers to type POS_T,
--p and q refer to an values of type POS_T,
--O refers to type OFF_T,
--o refers to a value of type OFF_T, and
--i refers to a value of type int.
_________________________
3) The conversion state is used for sequences that translate between
wide-character and generalized multibyte encoding, as described in
Amendment 1 to the C Standard.
Table 2--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) POS_T 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 POS_T + offset q-o == p |
|p += o |
+-----------------------------------------------------------------------------------------+
|q = p - o POS_T - offset q+o == p |
|p -= o |
+-----------------------------------------------------------------------------------------+
|o = p - q OFF_T distance q+o == p |
+-----------------------------------------------------------------------------------------+
6 The behavior of the stream after restoring the position with a POS_T
value modified using any other arithmetic operations is undefined.
7 The stream operations whose return type is POS_T may return
POS_T(OFF_T(-1)) as an invalid POS_T value to signal an error.
8 The conversion POS_T(OFF_T(-1)) constructs the invalid POS_T value,
which is available only for comparing to the return value of such mem
ber functions.
27.2 Forward declarations [lib.iostream.forward]
Header <iosfwd> synopsis
namespace std {
template<class charT> class basic_ios;
template<class charT> class basic_istream;
template<class charT> class basic_ostream;
typedef basic_ios<char> ios;
typedef basic_ios<wchar_t> wios;
typedef basic_istream<char> istream;
typedef basic_istream<wchar_t> wistream;
typedef basic_ostream<char> ostream;
typedef basic_ostream<wchar_t> wostream;
}
1 The template class basic_ios<charT,traits> serves as a base class for
the classes basic_istream<charT,traits> and
basic_ostream<charT,traits>.
2 The class ios is an instance of the template class basic_ios, special
ized by the type char.
3 The class wios is a version of the template class basic_ios special
ized by the type wchar_t.
27.3 Standard iostream objects [lib.iostream.objects]
Header <iostream> synopsis
#include <fstream>
namespace std {
extern istream cin;
extern ostream cout;
extern ostream cerr;
extern ostream clog;
extern wistream win;
extern wostream wout;
extern wostream werr;
extern wostream wlog;
}
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.
+------- BEGIN BOX 2 -------+
ISSUE: These objects need to be constructed and associations
established before dynamic initialization of file scope variables is
begun.
+------- END BOX 2 -------+
The objects are constructed, and the associations are established, the
first time an object of class basic_ios<charT,traits>::Init is con
structed. The objects are not destroyed during program execution.4)
27.3.1 Narrow stream objects [lib.narrow.stream.objects]
istream cin;
1 The object cin controls input from an unbuffered stream buffer associ
ated with the object stdin, declared in <cstdio>.
2 After the object cin is initialized, cin.tie() returns cout.
ostream cout;
3 The object cout controls output to an unbuffered stream buffer associ
ated with the object stdout, declared in <cstdio> (_lib.c.files_).
ostream cerr;
4 The object cerr controls output to an unbuffered stream buffer associ
ated with the object stderr, declared in <cstdio> (_lib.c.files_).
5 After the object cerr is initialized, cerr.flags() & unitbuf is
nonzero.
ostream clog;
6 The object clog controls output to a stream buffer associated with the
object stderr, declared in <cstdio> (_lib.c.files_).
+------- BEGIN BOX 3 -------+
ISSUE: The destination of clog ought to be implementation defined.
+------- END BOX 3 -------+
_________________________
4) Constructors and destructors for static objects can access these
objects to read input from stdin or write output to stdout or stderr.
27.3.2 Wide stream objects [lib.wide.stream.objects]
wistream win;
1 The object win controls input from an unbuffered stream buffer associ
ated with the object stdin, declared in <cstdio>.
2 After the object win is initialized, win.tie() returns wout.
wostream wout;
3 The object wout controls output to an unbuffered stream buffer associ
ated with the object stdout, declared in <cstdio> (_lib.c.files_).
wostream werr;
4 The object werr controls output to an unbuffered stream buffer associ
ated with the object stderr, declared in <cstdio> (_lib.c.files_).
5 After the object werr is initialized, werr.flags() & unitbuf is
nonzero.
wostream wlog;
6 The object wlog controls output to a stream buffer associated with the
object stderr, declared in <cstdio> (_lib.c.files_).
+------- BEGIN BOX 4 -------+
ISSUE: The destination of wlog ought to be implementation defined.
+------- END BOX 4 -------+
27.4 Iostreams base classes [lib.iostreams.base]
Header <ios> synopsis
#include <stdexcept> // for exception
namespace std {
typedef OFF_T streamoff;
typedef OFF_T wstreamoff;
typedef INT_T streamsize;
template <class charT> struct ios_traits<charT>;
struct ios_traits<char>;
struct ios_traits<wchar_t>;
class ios_base;
template<class charT, class traits = ios_traits<charT> >
class basic_ios;
typedef basic_ios<char> ios;
typedef basic_ios<wchar_t> wios;
// _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 type OFF_T (_lib.iostreams.off.t_).
typedef OFF_T wstreamoff;
2 The type wstreamoff is an implementation-defined type that satisfies
the requirements of type OFF_T (_lib.iostreams.off.t_).
typedef POS_T streampos;
3 The type streampos is an implementation-defined type that satisfies
the requirements of type POS_T (_lib.iostreams.pos.t_).
typedef POS_T wstreampos;
4 The type wstreampos is an implementation-defined type that satisfies
the requirements of type POS_T (_lib.iostreams.pos.t_).
typedef INT_T streamsize;
5 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.5)
27.4.2 Template struct ios_traits [lib.ios.traits]
namespace std {
template <class charT> struct ios_traits<charT> {
// _lib.ios.traits.types_ Types:
typedef charT char_type;
typedef INT_T int_type;
typedef POS_T pos_type;
typedef OFF_T off_type;
typedef To be specified state_type;
// _lib.ios.traits.values_ values:
static char_type eos();
static int_type eof();
static int_type not_eof(char_type c);
static char_type newline();
static size_t length(const char_type* s);
// _lib.ios.traits.tests_ tests:
static bool eq_char_type(char_type, char_type);
static bool eq_int_type (int_type, int_type);
static bool is_eof(int_type);
static bool is_whitespace(const ctype<char_type> ctype&, char_type c);
_________________________
5) 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).
// _lib.ios.traits.convert_ conversions:
static char_type to_char_type(int_type);
static int_type to_int_type (char_type);
static char_type* copy(char_type* dst, const char_type* src, size_t n) ;
static state_type get_state(pos_type pos);
static pos_type get_pos (streampos fpos, state_type state);
};
}
+------- BEGIN BOX 5 -------+
Issue: The newline() member needs to depend on a ctype<char_type>
parameter, just as does is_whitespace().
+------- END BOX 5 -------+
1 The template struct ios_traits<charT> is a traits class which main
tains the definitions of the types and functions necessary to imple
ment the iostream class templates. The template parameter charT rep
resents the character container type and each specialized version pro
vides the default definitions corresponding to the specialized charac
ter container type.
2 An implementation shall provide the following two instantiations of
ios_traits:
struct ios_traits<char>;
struct ios_traits<wchar_t>;
27.4.2.1 ios_traits types [lib.ios.traits.types]
state_type is an implementation-defined value-oriented type. It holds
the conversion state, and is compatible with the function
locale::codecvt().
27.4.2.2 ios_traits value functions [lib.ios.traits.values]
char_type eos();
Returns:
The null character which is used for the terminator of null termi
nated character strings. The default constructor for the character
container type provides the value.
int_type eof();
Returns:
an int_type value which represents the end-of-file. It is returned
by several functions to indicate end-of-file state (no more input
from an input sequence or no more output permitted to an output
sequence), or to indicate an invalid return value.
int_type not_eof(char_type c);
+------- BEGIN BOX 6 -------+
Should the argument type be int_type?
+------- END BOX 6 -------+
Returns:
a value other than the end-of-file, even if c==eof().
Notes:
It is used in basic_streambuf<charT,traits>::overflow().
Returns:
int_type(c) if c!=eof().
char_type newline();
Returns:
a character value which represent the newline character of the basic
character set.
Notes:
It appears as the default parameter of
basic_istream<charT,traits>::getline().
+------- BEGIN BOX 7 -------+
Issue: The newline() member needs to depend on a ctype<char_type>
parameter, just as does is_whitespace(). As such, we should overload
getline() with and without the parameter so that the caller need not
obtain a ctype<char_type> reference to pass to getline().
+------- END BOX 7 -------+
size_t length(const char_type* s);
Effects:
Determines the length of a null terminated character string pointed
to by s.
27.4.2.3 ios_traits test functions [lib.ios.traits.tests]
bool eq_char_type(char_type c1, char_type c2);
Returns:
true if c1 and c2 represent the same character.
bool eq_int_type(int_type c1, int_type c2);
Returns:
true if c1 and c2 represent the same character.
bool is_eof(int_type c);
Returns:
true if c represents the end-of-file.
bool is_whitespace(char_type c, const ctype<char_type>& ctype);
Returns:
true if c represents a whitespace character. The default definition
is as if it returns ctype.isspace(c). (See also
_lib.istream.prefix_)
1 An implementation of the iostream class templates may use all of the
above static member functions in addition to the following three func
tions provided from the base struct string_char_traits<CHAR_T>.
27.4.2.4 ios_traits conversion [lib.ios.traits.convert]
functions
char_type to_char_type(int_type c);
Effects:
Converts a valid character value represented in the int_type to the
corresponding char_type value. If c is the end-of-file value, the
return value is unspecified.
int_type to_int_type(char_type c);
Effects:
Converts a valid character value represented in the char_type to the
corresponding int_type value.
char_type* copy(char_type* dest, const char_type* src, size_t n);
Effects:
Copies n characters from the object pointed to by src into the
object pointed to by dest. If copying takes place between objects
that overlap, the behavior is undefined.
state_type get_state(pos_type pos);
Returns:
0.
+------- BEGIN BOX 8 -------+
To be specified.
+------- END BOX 8 -------+
pos_type get_pos(streampos fpos, state_type state);
Returns:
pos_type(pos).
+------- BEGIN BOX 9 -------+
To be specified.
+------- END BOX 9 -------+
27.4.3 Class ios_base [lib.ios.base]
namespace std {
class ios_base {
public:
class failure;
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.iostate.flags_ iostate flags:
iostate exceptions() const;
void exceptions(iostate except);
// _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);
int_type fill() const;
int_type fill(int_type ch);
int precision() const;
int precision(int prec);
int width() const;
int width(int 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);
protected:
ios_base();
private:
// static int index; exposition only
// int* iarray; exposition only
// void** parray; exposition only
};
}
+------- BEGIN BOX 10 -------+
Editorial proposal: Add the following declarations:
// _lib.iostate.flags_ iostate flags:
operator bool() 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;
ios_base& copyfmt(const ios_base& rhs);
Note that there will still be a version of copyfmt() specified for
basic_ios. The task of ``copying the state'' can be divided between
these two functions: ios_base::copyfmt() copies the current state of
the fmtflags, while basic_ios::copyfmt() copies the tie() state (if
that is indeed what is involved in copying the format).
+------- END BOX 10 -------+
+------- BEGIN BOX 11 -------+
Editorial proposal: Move the following to class basic_ios:
int_type fill() const;
int_type fill(int_type ch);
+------- END BOX 11 -------+
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;
--int* iarray, points to the first element of an arbitrary-length
integer 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]
27.4.3.1 Types [lib.ios.types]
27.4.3.1.1 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;
};
}
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:
what() == msg.str()
const char* what() const;
Returns:
The message msg with which the exception was created.
27.4.3.1.2 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 3:
Table 3--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; |
|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 4:
Table 4--fmtflags constants
+--------------------------------------+
| Constant Allowable values |
+--------------------------------------+
|adjustfield left | right | internal |
|basefield dec | oct | hex |
|floatfield scientific | fixed |
+--------------------------------------+
27.4.3.1.3 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 5:
Table 5--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.
27.4.3.1.4 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 6:
Table 6--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 |
+---------------------------------------------------+
27.4.3.1.5 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 7:
Table 7--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 |
+----------------------------------------------------------+
27.4.3.1.6 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_).
+------- BEGIN BOX 12 -------+
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.
+------- END BOX 12 -------+
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.narrow.stream.objects_), win, wout, werr, and wlog
(_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(), and clog.flush().
27.4.3.2 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().
int_type fill() const;
Returns:
The character to use to pad (fill) an output conversion to the spec
ified field width (_lib.ostream.formatted_).
int_type fill(int_type fillch);
Postcondition:
&fillch == fill().
Returns:
The previous value of fill().
int precision() const;
Returns:
The precision (number of digits after the decimal point) to generate
on certain output conversions.
int precision(int prec);
Postcondition:
prec == precision().
Returns:
The previous value of precision().
int width() const;
Returns:
The field width (number of characters) to generate on certain output
conversions.
int width(int wide);
Postcondition:
wide == width().
Returns:
The previous value of width().
27.4.3.3 ios_base locale functions [lib.ios.base.locales]
locale imbue(const locale loc);
Postcondition:
loc == getloc().
Returns:
The previous value of getloc().
locale getloc() const;
Returns:
The classic "C" locale if no locale has been imbued. Otherwise,
returns the locale in which to perform locale-dependent input and
output operations.
27.4.3.4 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 int 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.
Returns:
iarray[idx].
Notes:
After a subsequent call to iword(int) for the same object, the ear
lier return value may no longer be valid.6)
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.
Returns:
parray[idx].
Notes:
After a subsequent call to pword(int) for the same object, the ear
lier return value may no longer be valid.
27.4.3.5 ios_base constructors [lib.ios.base.cons]
ios_base();
Effects:
Constructs an object of class ios_base, assigning initial values to
its member objects. The postconditions of this function are indi
cated in Table 8:
_________________________
6) 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.
Table 8--ios_base() effects
+------------------------------------------------+
| Element Value |
+------------------------------------------------+
|rdstate() goodbit if sb is not a null |
| pointer, otherwise badbit. |
|exceptions() goodbit |
|flags() skipws | dec |
|width() zero |
|precision() 6 |
|fill() the space character |
|getloc() locale::classic() |
|index ??? |
|iarray a null pointer |
|parray a null pointer |
+------------------------------------------------+
+------- BEGIN BOX 13 -------+
ISSUE: The initialization of the value returned by getloc() remains an
open issue, as described in 95-0026/N0626; it may be changed to,
locale(), the global locale in effect at the time of initialization.
+------- END BOX 13 -------+
27.4.4 Template class basic_ios [lib.ios]
namespace std {
template<class charT, class traits = ios_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;
operator bool() 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;
// _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);
// _lib.ios.base.locales_ locales:
locale imbue(const locale& loc);
protected:
basic_ios();
void init(basic_streambuf<charT,traits>* sb);
};
}
+------- BEGIN BOX 14 -------+
Editorial proposal: Move the following declarations to class ios_base:
// _lib.iostate.flags_ iostate flags:
operator bool() 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;
+------- END BOX 14 -------+
+------- BEGIN BOX 15 -------+
Editorial proposal: Add the following to class basic_ios:
int_type fill() const;
int_type fill(int_type ch);
+------- END BOX 15 -------+
27.4.4.1 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_),
+------- BEGIN BOX 16 -------+
TBS
+------- END BOX 16 -------+
void init(basic_streambuf<charT,traits>* sb);
+------- BEGIN BOX 17 -------+
TBS
+------- END BOX 17 -------+
27.4.4.2 Member functions [lib.basic.ios.members]
basic_ostream<charT,traits>* tie() const;
Returns:
An output sequence that is tied to (synchronized with) an input
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().
+------- BEGIN BOX 18 -------+
Note: need to modify so as to describe the occurence of imbueing get
loc()::codecvt into the argument stream buffer.
+------- END BOX 18 -------+
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
rdbuf()->pubimbue(loc) (_lib.streambuf.locales_).
basic_ios& copyfmt(const basic_ios& rhs);
Effects:
Assigns to the member objects of *this the corresponding member
objects of rhs, except that:
--rdstate() is left unchanged;
--exceptions() is altered last by calling exception(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.
Returns:
*this.
27.4.4.3 basic_ios iostate flags functions [lib.iostate.flags]
operator bool() const
Returns:
!fail().
bool operator!() const
Returns:
fail().
iostate rdstate() const;
Returns:
The control state of the stream buffer.
void clear(iostate state = goodbit) throw(failure);
_________________________
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.
Postcondition:
state == rdstate().
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) throw(failure);
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;
Returns:
A mask that determines what elements set in rdstate() cause excep
tions to be thrown.
void exceptions(iostate except);
_________________________
8) Checking badbit also for fail() is historical practice.
Postcondition:
except == exceptions().
Effects:
Calls clear(rdstate()).
27.4.5 ios_base manipulators [lib.std.ios.manip]
27.4.5.1 fmtflags manipulators [lib.fmtflags.manip]
ios_base& boolalpha(ios_base& str);
Effects:
Calls str.setf(ios_base::boolalpha).
Returns:
str.9)
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.
Notes:
Does not affect any extractors.
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.
27.4.5.2 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.
27.4.5.3 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);
_________________________
9) The function signature dec(ios_base&) can be called by the function
signature basic_ostream& stream::operator<<(basic_ostream& (*)(ba
sic_ostream&)) to permit expressions of the form cout << dec to change
the format flags stored in cout.
Effects:
Calls str.setf(ios_base::oct, ios_base::basefield).
Returns:
str.
27.4.5.4 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
#include <ios> // for ios_traits
namespace std {
template<class charT, class traits = ios_traits<charT> >
class basic_streambuf;
typedef basic_streambuf<char> streambuf;
typedef basic_streambuf<wchar_t> wstreambuf;
}
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.
--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 = ios_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;
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:
int in_avail();
int_type snextc();
int_type sbumpc();
int_type sgetc();
int sgetn(char_type* s, streamsize n);
// _lib.streambuf.pub.pback_ Putback:
int_type sputbackc(char_type c);
int sungetc();
// _lib.streambuf.pub.put_ Put area:
int sputc(char_type c);
int_type 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 the return value of locale::classic().
_________________________
10) The default constructor is protected for class basic_streambuf to
assure that only objects for classes derived from this class may be
constructed.
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.
+------- BEGIN BOX 19 -------+
The choice of locale::classic() vs. locale() for the initial value of
getloc() remains open: 95-0026/N0626.
+------- END BOX 19 -------+
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 classic "C" locale locale::classic(). 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);
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]
int in_avail();
Returns:
If a read position is available, returns gend() - gnext(). 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().
Notes:
Uses traits::eof().
int_type sbumpc();
Returns:
If the input sequence read position is not available, returns
uflow(). Otherwise, returns char_type(*gptr()) and increments the
next pointer for the input sequence.
int_type sgetc();
Returns:
If the input sequence read position is not available, returns under
flow(). Otherwise, returns char_type(*gptr()).
int 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 c !=
gptr()[-1], returns pbackfail(c). Otherwise, decrements the next
pointer for the input sequence and returns *gptr().
int sungetc();
Returns:
If the input sequence putback position is not available, returns
pbackfail(). Otherwise, decrements the next pointer for the input
sequence and returns *gptr().
27.5.2.2.5 Put area [lib.streambuf.pub.put]
int sputc(char_type c);
Returns:
If the output sequence write position is not available, returns
overflow(c). Otherwise, stores c at the next pointer for the output
sequence, increments the pointer, and returns *pptr().
int_type 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 output 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.
Note:
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.virtuals_, _lib.filebuf.virtuals_).
Default behavior:
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::seekpos_,
_lib.filebuf::seekpos_).
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, and if gptr() is non-null, the
characters between gptr() and egptr() are restored to the input
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.
+------- BEGIN BOX 20 -------+
ISSUE: Is it possible to synchonize the input sequence in all cases?
If not, can we liberalize this specification to accomodate those con
straints?
+------- END BOX 20 -------+
27.5.2.4.3 Get area [lib.streambuf.virt.get]
int showmanyc();11)
+------- BEGIN BOX 21 -------+
ISSUE: Is this correct? 94-0035/N0422 said: ``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.
+------- END BOX 21 -------+
Returns:
a guaranteed lower bound on the number of characters that can be
read from the input sequence before a call to uflow() or underflow()
returns traits::eof(). A positive return value of indicates that
the next such call will not return traits::eof().12)
Default behavior:
Returns zero.
Notes:
Uses traits::eof().
_________________________
11) The morphemes of showmany are "es-how-many-see", not "show-manic".
12) The next such call might fail by throwing an exception. The in
tention is that the next call will return ``immediately.''
streamsize xsgetn(char_type* s, streamsize n);
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:
the first character of the pending sequence, if possible, without
moving the input sequence position past it. If the pending sequence
is null then the function fails.
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:
_________________________
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.
a)If the pending sequence is non-empty, egptr() is non-null and
egptr() - gptr() characters starting at gptr() are the characters in
the pending sequence
b)If the pending sequence is empty, either gptr() is null or gptr()
and egptr() are set to the same non-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)
Returns:
traits::eof() to indicate failure.
Default behavior:
Returns traits::eof().
int_type uflow();
Requires:
The constraints are the same as for underflow(), except that the
result character is transfered from the pending sequence to the
backup sequence, and the pending sequence may not be empty before
the transfer.
Default behavior:
Calls underflow(traits::eof()). If underflow() returns
traits::eof(), returns traits::eof(). Otherwise, does gbump(-1) and
returns *gptr().
Returns:
traits::not_eof(c).
Notes:
Uses traits::eof().
27.5.2.4.4 Putback [lib.streambuf.virt.pback]
int_type pbackfail(int c = traits::eof());
Notes:
The public functions of basic_streambuf call this virtual function
only when gptr() is null, gptr() == eback(), or *gptr() != c. Other
calls shall also satisfy that constraint.
The pending sequence is defined as for underflow(), with the modifi
cations that
--If c == traits::eof() then the input sequence is backed up one char
acter before the pending sequence is determined.
--If c != traits::eof() 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 successive elements of the array whose first element is desig
nated by s. Writing stops when either n characters have been writ
ten 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 c == traits::eof() 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 ba
sic_streambuf in this clause (_lib.stringbuf_, _lib.filebuf_), a spec
ification of how consuming a character effects the associated output
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 non-
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
#include <ios> // for ios_traits
namespace std {
template <class charT, class traits = ios_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
_________________________
sequence is given. There is no requirement on a program-defined
class.
15) Typically, overflow returns c to indicate success.
#include <ios> // for ios_traits
namespace std {
template <class charT, class traits = ioc_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
#include <istream>
#include <ostream>
namespace std {
typedef ? smanip;
smanip resetiosflags(ios_base::fmtflags mask);
smanip setiosflags (ios_base::fmtflags mask);
smanip setbase(int base);
smanip setfill(int c);
smanip setprecision(int n);
smanip setw(int n);
}
27.6.1 Input streams [lib.input.streams]
1 The header <istream> defines a type and a function signature that con
trol input from a stream buffer.
27.6.1.1 Template class basic_istream [lib.istream]
namespace std {
template <class charT, class traits = ios_traits<charT> >
class basic_istream : virtual public basic_ios<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.istream.cons_ Constructor/destructor:
explicit basic_istream(basic_streambuf<charT,traits>* sb);
virtual ~basic_istream();
// _lib.istream.prefix_ Prefix/suffix:
bool ipfx(bool noskipws = false);
void isfx();
// _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>>(char_type* s);
basic_istream<charT,traits>& operator>>(char_type& c);
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,
char_type delim = traits::newline());
basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>& sb,
char_type delim = traits::newline());
basic_istream<charT,traits>& getline(char_type* s, streamsize n,
char_type delim = traits::newline());
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);
};
}
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 except
that they do not invoke any virtual members of rdbuf() except uflow().
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::failure (_lib.iostate.flags_), before returning.
4 If one of these called functions throws an exception, then unless
explicitly noted otherwise the input function calls setstate(badbit)
and if badbit is on in exception() rethrows the exception without com
pleting its actions.
27.6.1.1.1 basic_istream constructors [lib.basic.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 basic_istream prefix and suffix [lib.istream.prefix]
bool ipfx(bool noskipws = false);
Effects:
If good() is true, prepares for formatted or unformatted input.
First, if tie() is not a null pointer, the function calls
tie()->flush() to synchronize the output sequence with any associ
ated external C stream.16) If noskipws is zero and flags() & skipws
is nonzero, the function extracts and discards each character as
long as the next available input character c is a whitespace charac
ter.
Notes:
The function basic_istream<charT,traits>::ipfx() uses the function
bool traits::is_whitespace(charT, const locale*) in the traits
structure to determine whether the next input character is
_________________________
16) The call tie()->flush() does not necessarily occur if the function
can determine that no synchronization is necessary.
whitespace or not.
1 To decide if the character c is a whitespace character, the function
performs ``as if'' it executes the following code fragment:
ctype<charT> ctype = getloc().use<ctype<charT> >();
if (traits::is_whitespace (c, ctype)!=0)
// c is a whitespace character.
Returns:
If, after any preparation is completed, good() is true, returns
true. Otherwise, it calls setstate(failbit) (which may throw
ios_base::failure (_lib.iostate.flags_)) and returns false.17)
2 [Example: A typical implementation of the ipfx() function may be as
follows:
template <class charT, class traits = ios_traits<charT> >
int basic_istream<charT,traits>::ipfx() {
...
// skipping whitespace according to a constraint function,
// is_whitespace
intT c;
typedef ctype<charT> ctype_type;
ctype_type& ctype = getloc().use<ctype_type>();
while ((c = rdbuf()->snextc()) != traits::eof()) {
if (!traits::is_whitespace (c,ctype)==0) {
rdbuf()->sputbackc (c);
break;
}
}
...
}
--end example]
3 When using ios_traits<char> or ios_traits<wchar_t>, the behavior of
the function traits::is_whitespace() is ``as if'' it invokes:
ctype = getloc().use<ctype<charT> >().is(ctype<charT>::space, c);
(see _lib.ios.traits.tests_); otherwise, the behavior of the function
traits::is_whitespace() is unspecified.
4 [Example: Those C++ programs that want to use locale-independent
whitespace predicate can specify their definition of is_whitespace in
their new ios_traits as follows:
struct my_traits : public ios_traits<char> {
typedef my_char_traits char_traits;
};
struct my_char_traits : public ios_traits<char> {
static bool is_whitespace (char c, const ctype<charT>& ctype) {
....(my own implementation)...
}
};
_________________________
17) The functions ipfx(int) and isfx() can also perform additional im
plementation-dependent operations.
--end example]
void isfx();
Effects:
None.
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 calling ipfx(). If
that function returns true, the function endeavors to obtain the
requested input. In any case, the formatted input function ends by
calling isfx(), then returns *this
2 Some formatted input functions endeavor to obtain the requested input
by parsing characters extracted from the input sequence, converting
the result to a value of some scalar data type, and storing the con
verted value in an object of that scalar data type.
3 The numeric conversion behaviors of the following extractors are
locale-dependent.
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);
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'' it performed
the following code fragment:
HOLDTYPE tmp;
num_get<charT>& fmt = loc.use< num_get<charT> >();
fmt.get (*this, 0, *this, loc, tmp);
if ((TYPE)tmp != tmp) { // set fail bit...
} else val = (TYPE)tmp;
In the above fragment, loc stands for the private member of the
basic_ios class, TYPE stands for the type of the argument of the
extractor, and HOLDTYPE is as follows;
--for short, int and long, HOLDTYPE is long;
--for unsigned short, unsigned int and unsigned long, HOLDTYPE is
unsigned long.
--for float, double, HOLDTYPE is double.
--for long double, HOLDTYPE is long double.
4 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. Class locale relies on this type as its
interface to istream, since the flexibility it has been abstracted
away from direct dependence on istream.
5 In case the converting result is a value of either an integral type (
short, unsigned short, int, unsigned int, long, unsigned long) or a
float type ( float, double, long double), performing to parse and con
vert the result depend on the imbued locale object. So the behavior
of the above type extractors are locale-dependent. The imbued locale
object uses an istreambuf_iterator to access the input character
sequence.
6 The behavior of such functions is described in terms of the conversion
specification ``as if'' for an equivalent call to the function
::fscanf()18) operating with the global locale set to getloc(), with
the following alterations:
--The formatted input function extracts characters from a stream
buffer, rather than reading them from an input file.19)
--If (flags() & skipws) == 0, the function does not skip any leading
white space. In that case, if the next input character is white
space, the scan fails.
--If the converted data value cannot be represented as a value of the
specified scalar data type, a scan failure occurs.
7 [Note: For conversion to an integral type other than a character type,
the function determines the integral conversion specifier as indicated
in Table 9:
_________________________
18) The signature fscanf(FILE*, const char*, ...) is declared in
<cstdio> (_lib.c.files_)
19) The stream buffer can, of course, be associated with an input
file, but it need not be.
Table 9--Integer conversions
+------------------------------------------------+
| State stdio equivalent |
+------------------------------------------------+
|(flags() & basefield) == oct %o |
+------------------------------------------------+
|(flags() & basefield) == hex %x |
|(flags() & uppercase) != 0 %X |
+------------------------------------------------+
|(flags() & basefield) == 0 %i |
+------------------------------------------------+
|Otherwise, |
+------------------------------------------------+
|signed integral type %d |
+------------------------------------------------+
|unsigned integral type %u |
+------------------------------------------------+
+------- BEGIN BOX 22 -------+
Is this table clear with regards to %x vs. %X?
+------- END BOX 22 -------+
+------- BEGIN BOX 23 -------+
Can the current num_put/num_get facet handle basefield specification?
Needs more discussion.
+------- END BOX 23 -------+
--end note]
8 If the scan fails for any reason, the formatted input function calls
setstate(failbit), which may throw ios_base::failure
(_lib.iostate.flags_).
27.6.1.2.2 basic_istream::operator>> [lib.istream::extractors]
basic_istream<charT,traits>& operator>>
(basic_istream<charT,traits>& (*pf)(basic_istream<charT,traits>&))
Returns:
pf(*this).20)
_________________________
20) See, for example, the function signature ws(basic_istream&)
(_lib.istream.manip_).
basic_istream<charT,traits>& operator>>
(basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));
Effects:
Calls pf(*this), then returns *this.21)
basic_istream<charT,traits>& operator>>(char_type* s);
Effects:
Extracts characters and stores them into successive locations of an
array whose first element is designated by s.22) If width() is
greater than zero, the maximum number of characters stored n is
width(); otherwise it is numeric_limits<int>::max() (_lib.limits_).
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;
--traits::is_whitespace(c,ctype) is true for the next available input
character c. In the above code fragment, the argument ctype is
acquired by getloc().use<ctype<charT> >().
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 location of
the array and calls width(0).
Returns:
*this.
Notes:
Uses traits::eos().
basic_istream<charT,traits>& operator>>(char_type& c);
Effects:
Extracts a character, if one is available, and stores it in c. Oth
erwise, the function calls setstate(failbit).
Returns:
*this.
basic_istream<charT,traits>& operator>>(bool& n);
_________________________
21) See, for example, the function signature
dec(basic_ios<charT,traits>&) (_lib.basefield.manip_).
22) Note that this function is not overloaded on types signed char and
unsigned char.
Effects:
Converts a boolean value, if one is available, and stores it in x.
Returns:
*this.
Notes:
Behaves as if:
getloc().use<num_get<charT,istreambuf_iterator<charT,traits> >().
get(*this, 0, *this, getloc(), n);
[Note: num_get<>::get() just sets the iostate flags, without check
ing whether failure() should be thrown; so operator>>() needs to
check that. --end note]
3 If flags.flag() & ios_base::boolalpha is false, num_get<>::get()
(_lib.category.numeric_) tries to read an integer value, which if
found must be 0 or 1; if the boolalpha flag is true, it reads charac
ters until it determines whether the numpunct<>::truename() or false
name() sequence23) is present. In either case if an exact match is
not found calls setstate(failbit).
basic_istream<charT,traits>& operator>>(short& n);
Effects:
Converts a signed short integer, if one is available, and stores it
in n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(unsigned short& n);
Effects:
Converts an unsigned short integer, if one is available, and stores
it in n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(int& n);
Effects:
Converts a signed integer, if one is available, and stores it in n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(unsigned int& n);
_________________________
23) The boolean value names for the default classic C" locale are
false" and true".
Effects:
Converts an unsigned integer, if one is available, and stores it in
n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(long& n);
Effects:
Converts a signed long integer, if one is available, and stores it
in n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(unsigned long& n);
Effects:
Converts an unsigned long integer, if one is available, and stores
it in n.
Returns:
*this.
basic_istream<charT,traits>& operator>>(float& f);
Effects:
Converts a float, if one is available, and stores it in f.
Returns:
*this.
basic_istream<charT,traits>& operator>>(double& f);
Effects:
Converts a double, if one is available, and stores it in f.
Returns:
*this.
basic_istream<charT,traits>& operator>>(long double& f);
Effects:
Converts a long double, if one is available, and stores it in f.
Returns:
*this.
basic_istream<charT,traits>& operator>>(void*& p);
Effects:
Converts a pointer to void, if one is available, and stores it in p.
Returns:
*this.
basic_istream<charT,traits>& operator>>
(basic_streambuf<charT,traits>* sb);
Requires:
sb shall be non-null.
Effects:
If sb is null, calls setstate(badbit), 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). set
state(badbit) is not called
4 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 calling ipfx(1).
If that function returns nonzero, the function endeavors to extract
the requested input. It also counts the number of characters
extracted. In any case, the unformatted input function ends by stor
ing the count in a member object and calling isfx(), then returning
the value specified for 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
function 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.24)
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 = traits::newline());
Effects:
Extracts characters and stores them into successive locations of an
array whose first element is designated by s.25) 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));
--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(basic_streambuf<char_type,traits>& sb,
char_type delim = traits::newline());
Effects:
Extracts characters and inserts them in the output sequence con
trolled by rdbuf(). Characters are extracted and inserted until any
of the following occurs:
_________________________
24) Note that this function is not overloaded on types signed charand
unsigned char.
25) Note that this function is not overloaded on types signed char and
unsigned char.
--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>& getline(char_type* s, streamsize n,
char_type delim = traits::newline());
Effects:
Extracts characters and stores them into successive locations of an
array whose first element is designated by s.26) 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);27)
3)n - 1 characters are stored (in which case the function calls set
state(failbit)).
4 These conditions are tested in the order shown.28)
5 If the function extracts no characters, it calls setstate(failbit)
(which may throw ios_base::failure (_lib.iostate.flags_)).29)
6 In any case, it then stores a null character (using traits::eos())
into the next successive location of the array.
Returns:
*this.
_________________________
26) Note that this function is not overloaded on types signed char and
unsigned char.
27) Since the final input character is ``extracted,'' it is counted in
the gcount(), even though it is not stored.
28) This allows an input line which exactly fills the buffer, without
setting failbit. This is different behavior than the historical AT&T
implementation.
29) This implies an empty input line will not cause failbit to be set.
7 [Example:
#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) || 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 '\n' in count
cout << "Line " << ++line_number;
}
cout << " (" << count << " chars): " << buffer << endl;
}
}
--end example]
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:
Extracts characters and stores them into successive locations of an
array whose first element is designated by s.30) Characters are
extracted and stored until either of the following occurs:
--n characters are stored;
--end-of-file occurs on the input sequence (in which case the function
calls setstate(failbit), which may throw ios_base::failure
(_lib.iostate.flags_)).
Returns:
*this.
streamsize readsome(char_type* s, streamsize n);
Effects:
Extracts characters and stores them into successive locations of an
array whose first element is designated by s.
Returns:
A value based on in_avail():
--If in_avail() < 0, calls setstate(eofbit) (which may throw
ios_base::failure (_lib.iostate.flags_)), and returns zero;
--If in_avail() == 0, returns zero;
--If in_avail() > 0, returns read(s, min(in_avail(),n)).
basic_istream<charT,traits>& putback(char_type c);
Effects:
Calls rdbuf->sputbackc(c). If that function returns traits::eof(),
calls setstate(badbit) (which may throw ios_base::failure
(_lib.iostate.flags_)).
Returns:
*this.
basic_istream<charT,traits>& unget();
Effects:
Calls rdbuf->sungetc(). If that function returns traits::eof(),
_________________________
30) Note that this function is not overloaded on types signed char and
unsigned char.
calls setstate(badbit) (which may throw ios_base::failure
(_lib.iostate.flags_)).
Returns:
*this.
int sync();
Effects:
If rdbuf() is a null pointer, returns traits::eof(). Otherwise,
calls rdbuf()->pubsync() and, if that function returns
traits::eof(), calls setstate(badbit) (which may throw
ios_base::failure (_lib.iostate.flags_), and returns traits::eof().
Otherwise, returns zero.
Notes:
Uses traits::eof().
pos_type tellg();
Returns:
if fail() == true, returns streampos(-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:
Skips any whitespace in the input sequence: saves a copy of
is.fmtflags, then clears is.skipws in is.flags(). Then calls
is.ipfx(), then is.isfx(), then restores is.flags() to its saved
value.
Returns:
is.
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 = ioc_traits<charT> >
class basic_ostream : virtual public basic_ios<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.ostream.cons_ Constructor/destructor:
explicit basic_ostream(basic_streambuf<char_type,traits>* sb);
virtual ~basic_ostream();
// _lib.ostream.prefix_ Prefix/suffix:
bool opfx();
void osfx();
// _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<<(const char_type* s);
basic_ostream<charT,traits>& operator<<(char_type c);
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<<(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();
pos_type tellp();
basic_ostream<charT,traits>& seekp(pos_type&);
basic_ostream<charT,traits>& seekp(off_type&, ios_base::seekdir);
};
}
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).
They may use other public members of basic_ostream except that they do
not invoke any virtual members of rdbuf() except overflow(). If the
called function throws an exception, the output function calls set
state(badbit), which may throw ios_base::failure
(_lib.iostate.flags_), and if badbit is on in exceptions() rethrows
the exception.
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 basic_ostream prefix and suffix [lib.ostream.prefix]
functions
bool opfx();
1 If good() is nonzero, prepares for formatted or unformatted output.
If tie() is not a null pointer, calls tie()->flush().31)
+------- BEGIN BOX 24 -------+
Note: Need to append the locale dependency on appropriate inserters.
In particular, descriptions must allow for digit group separators.
+------- END BOX 24 -------+
_________________________
31) The call tie()->flush() does not necessarily occur if the function
can determine that no synchronization is necessary.
Returns:
good().32)
void osfx();
2 If (flags() & unitbuf) != 0, calls flush().
pos_type tellp();
Returns:
if fail() == true, returns streampos(-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);
If fail() != true, executes rdbuf()->pubseekoff(off, dir).
Returns:
*this.
27.6.2.4 Formatted output functions [lib.ostream.formatted]
27.6.2.4.1 Common requirements [lib.ostream.formatted.reqmts]
1 Each formatted output function begins execution by calling opfx(). If
that function returns nonzero, the function endeavors to generate the
requested output. In any case, the formatted output function ends by
calling osfx(), then returning the value specified for the formatted
output function.
2 The numeric conversion behaviors of the following inserters are
locale-dependent (_lib.category.numeric_):
_________________________
32) The function signatures opfx() and osfx() can also perform addi
tional implementation-dependent operations.
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);
3 The classes num_get<> and num_put<> handle locale-dependent numeric
formatting and parsing. The above 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:
num_put<charT>& fmt = loc.use< num_put<charT> >();
fmt.put (ostreambuf_iterator(*this), *this, loc, val);
In the above fragment, loc stands for the private member of the
basic_ios class which maintains the imbued localeobject. The first
argument provides an object of the ostreambuf_iterator class which is
an iterator for ostream class. It bypasses ostreams and uses stream
bufs 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.
4 Some formatted output functions endeavor to generate the requested
output by converting a value from some scalar or NTBS type to text
form and inserting the converted text in the output sequence.
+------- BEGIN BOX 25 -------+
Needs work: NTBS.
+------- END BOX 25 -------+
The behavior of such functions is described in terms of the conversion
specification ``as if'' for an equivalent call to the function
::fprintf(),33) operating with the global locale set to getloc(), with
the following alterations:
--The formatted output function inserts characters in a stream buffer,
rather than writing them to an output file.34)
--The formatted output function uses the fill character returned by
fill() as the padding character (rather than the space character for
left or right padding, or 0 for internal padding).
5 If the operation fails for any reason, the formatted output function
calls setstate(badbit), which may throw ios_base::failure
_________________________
33) The signature fprintf(FILE*, const char_type*, ...) is declared
in <cstdio> (_lib.c.files_).
34) The stream buffer can, of course, be associated with an output
file, but it need not be.
(_lib.iostate.flags_).
6 [Note: For conversion from an integral type other than a character
type, the function determines the integral conversion specifier as
indicated in Table 10:
Table 10--Integer conversions
+------------------------------------------------+
| State stdio equivalent |
+------------------------------------------------+
|(flags() & basefield) == oct %o |
+------------------------------------------------+
|(flags() & basefield) == hex %x |
|(flags() & uppercase) != 0 %X |
+------------------------------------------------+
|Otherwise, |
+------------------------------------------------+
|signed integral type %d |
+------------------------------------------------+
|unsigned integral type %u |
+------------------------------------------------+
+------- BEGIN BOX 26 -------+
Is this table clear with regards to %x vs. %X?
+------- END BOX 26 -------+
+------- BEGIN BOX 27 -------+
Can the current num_put/num_get facet handle basefield specification?
Needs more discussion.
+------- END BOX 27 -------+
--end note]
7 [Note: For conversion from a floating-point type, the function deter
mines the floating-point conversion specifier as indicated in Table
11:
Table 11--Floating-point conversions
+--------------------------------------------------------+
| State stdio equivalent |
+--------------------------------------------------------+
|(flags() & floatfield) == fixed %f |
+--------------------------------------------------------+
|(flags() & floatfield) == scientific %e |
|(flags() & uppercase) != 0 %E |
+--------------------------------------------------------+
|Otherwise, |
+--------------------------------------------------------+
| %g |
|(flags() & uppercase) != 0 %G |
+--------------------------------------------------------+
+------- BEGIN BOX 28 -------+
Is this table clear with regards to %e vs. %E?
+------- END BOX 28 -------+
--end note]
8 [Note: The conversion specifier has the following additional quali
fiers prepended as indicated in Table 12:
Table 12--Floating-point conversions
+----------------------------------------------------------------------+
| Type(s) State stdio equivalent |
+----------------------------------------------------------------------+
|an integral type oth (flags() & showpos) != 0 + |
|er than a character (flags() & showbase) != 0 # |
|type |
+----------------------------------------------------------------------+
|a floating-point type (flags() & showpos) != 0 + |
| (flags() & showpoint) != 0 # |
+----------------------------------------------------------------------+
--end note]
9 [Note: For any conversion, if width() is nonzero, then a field width
is specified in the conversion specification. The value is width().
--end note]
10For conversion from a floating-point type, if (flags() & fixed) != 0
or if precision() > 0, then precision() is specified in the conversion
specification.
11[Note: Moreover, for any conversion, padding with the fill character
returned by fill() behaves as indicated in Table 13:
Table 13--Fill padding
+------------------------------------------------------------------------------------+
| State Justification fprintf flag,padding |
+------------------------------------------------------------------------------------+
|(flags() & adjustfield)==left left (pad after text) (none), space padding |
+------------------------------------------------------------------------------------+
|(flags() & adjustfield)==internal internal 0, zero padding35) |
+------------------------------------------------------------------------------------+
|Otherwise right (pad before text) -, space padding |
+------------------------------------------------------------------------------------+
--end note]
12Unless explicitly stated otherwise for a particular inserter, each
formatted output function calls width(0) after determining the field
width.
27.6.2.4.2 basic_ostream::operator<< [lib.ostream.inserters]
basic_ostream<charT,traits>& operator<<
(basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&))
Returns:
pf(*this).36)
basic_ostream<charT,traits>& operator<<
(basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&))
Effects:
Calls pf(*this).
Returns:
*this.37)
basic_ostream<charT,traits>& operator<<(const char_type* s);
Requires:
s shall be a null-terminated byte string.
_________________________
35) The conversion specification #o generates a leading 0 which is not
a padding character.
36) See, for example, the function signature endl(basic_ostream&)
(_lib.ostream.manip_) .
37) See, for example, the function signature dec(ios_base&)
(_lib.basefield.manip_).
Effects:
Converts the NTBS s with the conversion specifier s.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(char_type c);
Effects:
Converts the char_type c with the conversion specifier c and a field
width of zero.38)
Notes:
The stored field width ( basic_ios<charT,traits>::width()) is not
set to zero.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(bool n);
1 Behaves as if:
getloc().use<num_put<charT,istreambuf_iterator<charT,traits> >()
.put(*this, *this, getloc(), n);
which writes out a 0 or 1, or the results of get
loc().use<numpunct<charT> >().truename() or falsename()
(_lib.category.numeric_), according as whether the boolalpha flag is
set.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(short n);
Effects:
Converts the signed short integer n with the integral conversion
specifier preceded by h.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(unsigned short n);
Effects:
Converts the unsigned short integer n with the integral conversion
specifier preceded by h.
Returns:
*this.
_________________________
38) Note that this function is not overloaded on types signed char and
unsigned char.
basic_ostream<charT,traits>& operator<<(int n);
Effects:
Converts the signed integer n with the integral conversion speci
fier.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(unsigned int n);
Effects:
Converts the unsigned integer n with the integral conversion speci
fier.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(long n);
Effects:
Converts the signed long integer n with the integral conversion
specifier preceded by l.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(unsigned long n);
Effects:
Converts the unsigned long integer n with the integral conversion
specifier preceded by l.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(float f);
Effects:
Converts the float f with the floating-point conversion specifier.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(double f);
Effects:
Converts the double f with the floating-point conversion specifier.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(long double f);
Effects:
Converts the long double f with the floating-point conversion speci
fier preceded by L.
Returns:
*this.
basic_ostream<charT,traits>& operator<<(void* p);
Effects:
Converts the pointer to void p with the conversion specifier p.
Returns:
*this.
basic_ostream<charT,traits>& operator<<
(basic_streambuf<charT,traits>* sb);
Effects:
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);
--an exception occurs while getting a character from sb (in which
case, the exception is rethrown).
2 If the function inserts no characters or if it stopped because an
exception was thrown while extracting a character, it calls set
state(failbit) (which may throw ios_base::failure
(_lib.iostate.flags_)). If an exception was thrown while extracting a
character and failbit is on in exceptions() the caught exception is
rethrown.
Returns:
*this.
27.6.2.5 Unformatted output functions [lib.ostream.unformatted]
1 Each unformatted output function begins execution by calling opfx().
If that function returns nonzero, the function endeavors to generate
the requested output. In any case, the unformatted output function
ends by calling osfx(), then returning the value specified for the
unformatted output function.
basic_ostream<charT,traits>& put(char_type c);
Effects:
Inserts the character c, if possible.39)
2 Otherwise, calls setstate(badbit) (which may throw ios_base::failure
(_lib.iostate.flags_)).
Returns:
*this.
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.40) 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 traits::eof(), calls setstate(badbit) (which may
throw ios_base::failure (_lib.iostate.flags_)).
Returns:
*this.
27.6.2.6 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(traits::newline()), then os.flush().
Returns:
os.41)
_________________________
39) Note that this function is not overloaded on types signed char and
unsigned char.
40) Note that this function is not overloaded on types signed char and
unsigned char.
41) The effect of executing cout << endl is to insert a newline char
acter in the output sequence controlled by cout, then synchronize it
namespce std {
template<class charT, class traits>
basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os);
}
Effects:
Inserts a null character into the output sequence: calls
os.put(traits::eos()).
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 smanip is an implementation-defined function type (_dcl.fct_)
returned by the standard manipulators.
smanip resetiosflags(ios_base::fmtflags mask);
Returns:
smanip(f, mask), where f can be defined as:42)
template<class charT, class traits>
ios_base& f(ios_base& str, ios_base::fmtflags mask)
{ // reset specified flags
str.setf(ios_base::fmtflags(0), mask);
return str;
}
_________________________
with any external file with which it might be associated.
42) 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:
smanip(f,mask), where f can be defined as:
ios_base& f(ios_base& str, ios_base::fmtflags mask)
{ // set specified flags
str.setf(mask);
return str;
}
smanip setbase(int base);
Returns:
smanip(f, base), 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;
}
smanip setfill(int c);
Returns:
smanip(f, c), where f can be defined as:
ios_base& f(ios_base& str, int c)
{ // set fill character
str.fill(c);
return str;
}
smanip setprecision(int n);
Returns:
smanip(f, n), where f can be defined as:
ios_base& f(ios_base& str, int n)
{ // set precision
str.precision(n);
return str;
}
smanip setw(int n);
Returns:
smanip(f, n), where f can be defined as:
ios_base& f(ios_base& str, int n)
{ // set width
str.width(n);
return str;
}
27.7 String-based streams [lib.string.streams]
1 The header <sstream> defines three template classes, and six types,
that associate stream buffers with objects of class basic_string, as
described in subclause _lib.string.classes_.
Header <sstream> synopsis
#include <streambuf>
#include <istream>
#include <ostream>
namespace std {
template <class charT, class traits = int_charT_traits<charT> >
class basic_stringbuf;
typedef basic_stringbuf<char> stringbuf;
typedef basic_stringbuf<wchar_t> wstringbuf;
template <class charT, class traits = ios_traits<charT> >
class basic_istringstream;
typedef basic_istringstream<char> istringstream;
typedef basic_istringstream<wchar_t> wistringstream;
template <class charT, class traits = ios_traits<charT> >
class basic_ostringstream;
typedef basic_ostringstream<char> ostringstream;
typedef basic_ostringstream<wchar_t> wostringstream;
}
Table 13--Header <cstdlib> synopsis
+---------------------+
|Type Name(s) |
+---------------------+
|Functions: |
| atof stroul |
| atoi strtod |
| atol strtol |
+---------------------+
2
SEE ALSO: ISO C subclause 7.10.1.
27.7.1 Template class basic_stringbuf [lib.stringbuf]
namespace std {
template <class charT, class traits = int_charT_traits<charT> >
class basic_stringbuf : public basic_streambuf<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.stringbuf.cons_ Constructors:
explicit basic_stringbuf(ios_base::openmode which
= ios_base::in | ios_base::out);
explicit basic_stringbuf(const basic_string<char_type>& str,
ios_base::openmode which
= ios_base::in | ios_base::out);
// _lib.stringbuf.members_ Get and set:
basic_string<char_type> str() const;
void str(const basic_string<char_type>& 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 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.
+------- BEGIN BOX 29 -------+
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.
+------- END BOX 29 -------+
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<char_type>& 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(), initializing the base class with
basic_streambuf() (_lib.streambuf.cons_), and initializing mode with
which.
Postconditions:
str() == str. If str.size() > 0, sets the get and/or put pointers
as indicated in Table 14:
Table 14--str get/set areas
+------------------------------------------------------------------+
| Condition Setting |
+------------------------------------------------------------------+
|(which & ios_base::in) != 0 setg(str(),str(),str()+str.size()) |
+------------------------------------------------------------------+
|(which & ios_base::out) != 0 setp(str(),str(),str()+str.size()) |
+------------------------------------------------------------------+
27.7.1.2 Member functions [lib.stringbuf.members]
basic_string<char_type> str() const;
Returns:
The return value of this function are indicated in Table 15:
Table 15--str return values
+---------------------------------------------------------------------------+
| Condition Return Value |
+---------------------------------------------------------------------------+
|(mode & basic_ios::in) basic_string<char_type>(eback(),egptr()-eback()) |
|!= 0 and (gptr() != 0) |
+---------------------------------------------------------------------------+
|(mode & basic_ios::out) basic_string<char_type>(pbase(),pptr()-pbase()) |
|!= 0 and (pptr() != 0) |
+---------------------------------------------------------------------------+
|Otherwise basic_string<char_type>() |
+---------------------------------------------------------------------------+
void str(const basic_string<char_type>& s);
Effects:
If s.length() is zero, executes:
setg(0, 0, 0);
setp(0, 0);
Postcondition:
str() == s. If str.size() > 0, sets the get and/or put pointers as
indicated in Table 16:
Table 16--str get/set areas
+------------------------------------------------------------------+
| Condition Setting |
+------------------------------------------------------------------+
|(which & ios_base::in) != 0 setg(str(),str(),str()+str.size()) |
+------------------------------------------------------------------+
|(which & ios_base::out) != 0 setp(str(),str(),str()+str.size()) |
+------------------------------------------------------------------+
27.7.1.3 Overridden virtual functions [lib.stringbuf.virtuals]
int_type underflow();
Returns:
If the input sequence has a read position available, returns
char_type(*gptr()).
Otherwise, returns traits::eof().
int_type pbackfail(int_type c = traits::eof());
+------- BEGIN BOX 30 -------+
Check vs. _lib.streambuf.virtuals_ and _lib.filebuf.virtuals_
+------- END BOX 30 -------+
Effects:
Puts back the character designated by c to the input sequence, if
possible, in one of three ways:
--If c != traits::eof(), if the input sequence has a putback position
available, and if char_type(c) == char_type(gptr()[-1]), assigns
gptr() - 1 to gptr().
Returns: c.
--If c != traits::eof(), if the input sequence has a putback position
available, and if mode & ios_base::out is nonzero, assigns c to
*--gptr().
Returns: char_type(c).
--If c == traits::eof() and if the input sequence has a putback posi
tion available, assigns gptr() - 1 to gptr().
Returns: char_type(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 c != traits::eof() 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 c == traits::eof(), 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 [Note: 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 suf
ficient 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()).
--end note]
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
+------- BEGIN BOX 31 -------+
Check vs. _lib.filebuf.virtuals_
+------- END BOX 31 -------+
Effects:
Alters the stream position within one of the controlled sequences,
if possible, as indicated in Table 17:
Table 17--seekoff positioning
+----------------------------------------------------------------------------------+
| Conditions Result |
+----------------------------------------------------------------------------------+
|(which & basic_ios::in) != 0 positions the input sequence |
+----------------------------------------------------------------------------------+
|(which & basic_ios::out) != 0 positions the output sequence |
+----------------------------------------------------------------------------------+
|Otherwise, |
|(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 18:
Table 18--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);
+------- BEGIN BOX 32 -------+
Check vs. _lib.filebuf.virtuals_
+------- END BOX 32 -------+
Effects:
Alters the stream position within one of the controlled sequences,
if possible, 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 the function positions neither sequence, the positioning opera
tion fails.
4 For a sequence to be positionedif its next pointer (either gptr() or
pptr()) is a null pointer, the positioning operation fails.
Otherwise, the function determines newoff from sp.offset():
--If newoff is an invalid stream position, has a negative value, or
has a value greater than (xend - xbeg), the positioning operation
fails.
--Otherwise, the function adds newoff to the beginning pointer xbeg
and stores the result in 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.
27.7.2 Template class basic_istringstream [lib.istringstream]
namespace std {
template <class charT, class traits = ios_traits<charT> >
class basic_istringstream : public basic_istream<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.istringstream.cons_ Constructors:
explicit basic_istringstream(ios_base::openmode which = ios_base::in);
explicit basic_istringstream(const basic_string<charT>& str,
ios_base::openmode which = ios_base::in);
// _lib.istringstream.members_ Members:
basic_stringbuf<charT,traits>* rdbuf() const;
basic_string<charT> str() const;
void str(const basic_string<charT>& s);
private:
// basic_stringbuf<charT,traits> sb; exposition only
};
}
1 The class basic_istringstream<charT,traits> supports reading objects
of class basic_string<charT,traits>. 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.
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>(which))
(_lib.stringbuf.cons_).
explicit basic_istringstream(const basic_string<charT>& 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>(str, which))
(_lib.stringbuf.cons_).
27.7.2.2 Member functions [lib.istringstream.members]
basic_stringbuf<charT,traits>* rdbuf() const;
Returns:
(basic_stringbuf<charT,traits>*)&sb.
basic_string<charT> str() const;
Returns:
rdbuf()->str().
void str(const basic_string<charT>& s);
Effects:
Calls rdbuf()->str(s).
27.7.2.3 Class basic_ostringstream [lib.ostringstream]
namespace std {
template <class charT, class traits = ios_traits<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>& str,
ios_base::openmode which = ios_base::out);
virtual ~basic_ostringstream();
// _lib.ostringstream.members_ Members:
basic_stringbuf<charT,traits>* rdbuf() const;
basic_string<charT> str() const;
void str(const basic_string<charT>& s);
private:
// basic_stringbuf<charT,traits> sb; exposition only
};
}
1 The class basic_ostringstream<charT,traits> supports writing objects
of class basic_string<charT,traits>. 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.
27.7.2.4 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>(which)) (_lib.stringbuf.cons_).
explicit basic_ostringstream(const basic_string<charT>& 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>(str, which))
(_lib.stringbuf.cons_).
27.7.2.5 Member functions [lib.ostringstream.members]
basic_stringbuf<charT,traits>* rdbuf() const;
Returns:
(basic_stringbuf<charT,traits>*)&sb.
basic_string<charT> str() const;
Returns:
rdbuf()->str().
void str(const basic_string<charT>& s);
Effects:
Calls rdbuf()->str(s).
27.8 File-based streams [lib.file.streams]
27.8.1 File streams [lib.fstreams]
1 The header <fstream> defines three class templates, and six types,
that associate stream buffers with files and assist reading and writ
ing files.
Header <fstream> synopsis
#include <streambuf>
#include <istream>
#include <ostream>
namespace std {
template <class charT, class traits = ios_traits<charT> >
class basic_filebuf;
typedef basic_filebuf<char> filebuf;
typedef basic_filebuf<wchar_t> wfilebuf;
template <class charT, class traits = ios_traits<charT> >
class basic_ifstream;
typedef basic_ifstream<char> ifstream;
typedef basic_ifstream<wchar_t> wifstream;
template <class charT, class traits = ios_traits<charT> >
class basic_ofstream;
typedef basic_ofstream<char> ofstream;
typedef basic_ofstream<wchar_t> wofstream;
}
+------- BEGIN BOX 33 -------+
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 33 -------+
2 In this subclause, the type name FILE is a synonym for the type
FILE.43)
--File A File provides an external source/sink stream whose underlaid
character type is char (byte).44)
_________________________
43) FILE is defined in <cstdio> (_lib.c.files_).
44) 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.
--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-
oriented filebuf, namely wfilebuf should convert wide character
sequences. Because of necessity of the conversion between the
external source/sink streams and wide character sequences.
27.8.1.1 Template class basic_filebuf [lib.filebuf]
namespace std {
template <class charT, class traits = ios_traits<charT> >
class basic_filebuf : public basic_streambuf<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.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 int showmanyc();
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(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 or for update, the input
sequence cannot be read.
--If the file is not open for writing or for update, the output
sequence cannot be written.
--A joint file position is maintained for both the input sequence and
the output sequence.
4 In order to support file I/O and multibyte/wide character conversion,
conversions are performed using getloc(). Specifically:
--when input is performed, bytes are read from the file and converted
to charT ``as if'' by using
getloc().use<codecvt<char,charT,ios_traits::state_type> >()
--when output is performed, charT's are converted to char ``as if'' by
using
getloc().use<codecvt<charT,char,ios_traits::state_type> >().
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 the associated file is available and open.
basic_filebuf<charT,traits>* open(const char* s, ios_base::openmode mode);
Effects:
If is_open() == false, returns a null pointer. Otherwise, calls
basic_streambuf<charT,traits>::basic_streambuf()
(_lib.streambuf.cons_).
It then opens a file, if possible, whose name is the NTBS s (``as
if'' by calling ::fopen(s,modstr)).
[Note: The NTBS modstr is determined from mode & ~ios_base::ate as
indicated in Table 19:
Table 19--File open modes
+---------------------------------------------+
| ios_base stdio equivalent |
| Value(s) |
+---------------------------------------------+
|in "r" |
|out | trunc "w" |
|out | app "a" |
|in | out "r+" |
|in | binary "rb" |
|out | trunc | binary "wb" |
|out | app | binary "ab" |
|in | out "r+ |
|in | out | trunc "w+" |
|in | out | app "a+" |
|in | out | binary "r+b" |
|in | out | trunc | binary "w+b" |
|in | out | app | binary "a+b" |
+---------------------------------------------+
--end note]
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)).45)
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();
Effects:
If is_open() == false, returns a null pointer. Otherwise, closes
the file (``as if'' by calling ::fclose(file)).46)
Returns:
this on success, a null pointer otherwise.
_________________________
45) 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_).
46) The function signature fclose(FILE*) is declared, in <cstdio>
(_lib.c.files_).
Postcondition:
is_open() == false.
27.8.1.4 Overridden virtual functions [lib.filebuf.virtuals]
int showmanyc();
Requires:
is_open() == true.
Effects:
Behaves the same as basic_streambuf::showmanyc()
(_lib.streambuf.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();
Requires:
is_open() == true.
Effects:
Behaves according to the description of
basic_streambuf<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 (
from_buf) and then ``as if'' doing
char from_buf[FSIZE];
char* from_end;
charT to_buf[TSIZE];
charT* to_end;
codecvt_base::result r
= getloc().use<codecvt<char,charT,typename ios_traits::state_type> >().
convert(st,from_buf,from_buf+FSIZE,from_end,
to_buf, to_buf+to_size, to_end);
This must be done in such a way that the class can recover the posi
tion ( fpos_t) corresponding to each character between to_buf and
to_end. If the value of r indicates that convert() ran out of space
in to_buf, retry with a larger to_buf.
int_type pbackfail(int_type c = traits::eof());
+------- BEGIN BOX 34 -------+
Check vs. _lib.streambuf.virtuals_.
+------- END BOX 34 -------+
Requires:
is_open() == true.
Effects:
Puts back the character designated by c to the input sequence, if
possible, in one of four ways:
--If c != traits::eof() and if the function makes a putback position
available and if char_type(c) == char_type(gptr()[-1]), decrements
the next pointer for the input sequence, gptr().
--If c != traits::eof() 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.
--If c == traits::eof() and if either the input sequence has a putback
position available or the function makes a putback position avail
able, decrements the next pointer for the input sequence, gptr().
Returns:
traits::eof() to indicate failure, otherwise c.
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.
Default behavior:
Returns traits::eof().
int_type overflow(int_type c = traits::eof());
Requires:
is_open() == true.
Effects:
Behaves according to the description of
basic_streambuf<charT,traits>::overflow(c), except that the behavior
of ``consuming characters'' is performed by first coverting ``as
if'' by:
charT* b = pbase();
charT* p = pptr();
charT* end;
char buf[BSIZE];
char* ebuf;
codecvt_base::result r
= getloc().use<codecvt<charT, char, ios_traits::state_type> >().
convert(st,b(),p(),end,buf,buf+BSIZE,ebuf);
and then
--If r == codecvt_base::error then fail.
--If r == codecvt_base::noconv then output chararcters from b upto
(and not including) p.
--If r == codecvt_base::partial then output to the file characters
from buf upto ebuf, and repeat using characters from end to p. If
output fails, fail (without repeating).
--Otherwise output from buf to ebuf, 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::eof() to indicate failure. If is_open() == false, the func
tion always fails.
basic_streambuf* setbuf(char_type* s, int n);
+------- BEGIN BOX 35 -------+
[To Be Filled]
Check vs. _lib.streambuf.virtuals_ and _lib.stringbuf.virtuals_.
+------- END BOX 35 -------+
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
Requires:
is_open() == true.
Effects:
The current state is determined as follows: If the the last opera
tion was overflow(), the current state is obtained by combining the
shiftstate contained in st with the current position ( fpos_t) of
the file. If the last operation was underflow(), the shiftstate and
file position are determined (according to whatever means they were
saved by underflow()) as corresponding to pptr().
Then, alters the stream position within the controlled sequences, if
possible, as described below.
If is_open() == false, the positioning operation fails. Otherwise,
repositions within the associated file (``as if'' by calling
::fseek(file,off,whence).47)
[Note: The function determines one of three values for the argument
whence, of type int, as indicated in Table 20:
_________________________
47) 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_).
Table 20--seekoff effects
+----------------------------------+
| way Value stdio Equivalent |
+----------------------------------+
|basic_ios::beg SEEK_SET |
|basic_ios::cur SEEK_CUR |
|basic_ios::end SEEK_END |
+----------------------------------+
--end note]
The function extracts the conversion state from off by means of
get_offstate() to reset the rdstate() member.
+------- BEGIN BOX 36 -------+
The member get_offstate() is not defined anywhere.
+------- END BOX 36 -------+
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.iostreams.pos.t_).
pos_type seekpos(pos_type sp, ios_base::openmode which
= ios_base::in | ios_base::out);
+------- BEGIN BOX 37 -------+
[To Be Filled]
Check vs. _lib.streambuf.virtuals_ and _lib.stringbuf.virtuals_.
+------- END BOX 37 -------+
Requires:
is_open() == true.
int sync();
+------- BEGIN BOX 38 -------+
[To Be Filled]
Check vs. _lib.streambuf.virtuals_.
+------- END BOX 38 -------+
void imbue(const locale& loc);
Effects:
Calls sync() and if sync() fails, sets a flag and the next call to
any virtual will fail.
27.8.1.5 Template class basic_ifstream [lib.ifstream]
namespace std {
template <class charT, class traits = file_traits<charT> >
class basic_ifstream : public basic_istream<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.ifstream.cons_ Constructors:
basic_ifstream();
explicit basic_ifstream(const char* s, openmode mode = 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.filebuf.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_filebuf<charT,traits>()) (_lib.istream.cons_,
_lib.filebuf.cons_), then calls rdbuf()->open(s,mode).
27.8.1.7 Member functions [lib.ifstream.members]
explicit 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 = in);
Effects:
Calls rdbuf()->open(s,mode). If is_open() returns false, calls set
state(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 = file_traits<charT> >
class basic_ofstream : 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.ofstream.cons_ Constructors:
basic_ofstream();
explicit basic_ofstream(const char* s, openmode mode = out);
// _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>, initial
izing 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.filebuf.cons_), then calls rdbuf()->open(s, mode).
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). If is_open() is then false, calls set
state(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_)).
27.8.2 C Library files [lib.c.files]
1 Headers <cstdio>, and <cwchar>.
Table 20--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 tmpfile |
|fclose fopen fseek perror scanf tmpnam |
|feof fprintf fsetpos printf setbuf ungetc |
|ferror fputc ftell putc setvbuf vprintf |
|fflush fputs fwrite puts sprintf vprintf |
|fgetc fread getc remove sscanf vsprintf |
|fgetpos freopen getchar rename tmpfile |
+-------------------------------------------------------------------------------+
Table 20--Header <cwchar> synopsis
+------------------------------------------------------------------------+
| Type Name(s) |
+------------------------------------------------------------------------+
|Macros: NULL <cwchar> WCHAR_MAX WCHAR_MIN WEOF <cwchar> |
+------------------------------------------------------------------------+
|Types: mbstate_t wint_t <cwchar> |
+------------------------------------------------------------------------+
|Struct: tm <cwchar> |
+------------------------------------------------------------------------+
|Functions: |
|btowc getwchar ungetwc wcscpy wcsrtombs wmemchr |
|fgetwc mbrlen vfwprintf wcscspn wcsspn wmemcmp |
|fgetws mbrtowc vswprintf wcsftime wcsstr wmemcpy |
|fputwc mbsinit vwprintf wcslen wcstod wmemmove |
|fputws mbsrtowcs wcrtomb wcsncat wcstok wmemset |
|fwide putwc wcscat wcsncmp wcstol wprintf |
|fwprintf putwchar wcschr wcsncpy wcstoul wscanf |
|fwscanf swprintf wcscmp wcspbrk wcsxfrm |
|getwc swscanf wcscoll wcsrchr wctob |
+------------------------------------------------------------------------+
2 The contents are the same as the Standard C library, except that none
of the headers defines wchar_t.
SEE ALSO: ISO C subclause 7.9, Amendment 1 subclause 4.6.2.