D.14 [depr.str.strstreams] char* streams

D.14.1 [depr.strstream.syn] Header <strstream> synopsis

1 The header <strstream> defines types that associate stream buffers with character array objects and assist reading and writing such objects.

namespace std {
    class strstreambuf;
    class istrstream;
    class ostrstream;
    class strstream;
}

D.14.2 [depr.strstreambuf] Class strstreambuf

D.14.2.1 [depr.strstreambuf.general] General

namespace std {
  class strstreambuf : public basic_streambuf<char> {
  public:
    strstreambuf() : strstreambuf(0) {}
    explicit strstreambuf(streamsize alsize_arg);
    strstreambuf(void* (*palloc_arg)(size_t), void (*pfree_arg)(void*));
    strstreambuf(char* gnext_arg, streamsize n, char* pbeg_arg = nullptr);
    strstreambuf(const char* gnext_arg, streamsize n);
    strstreambuf(signed char* gnext_arg, streamsize n,
                 signed char* pbeg_arg = nullptr);
    strstreambuf(const signed char* gnext_arg, streamsize n);
    strstreambuf(unsigned char* gnext_arg, streamsize n,
                 unsigned char* pbeg_arg = nullptr);
    strstreambuf(const unsigned char* gnext_arg, streamsize n);

    virtual ~strstreambuf();

    void  freeze(bool freezefl = true);
    char* str();
    int   pcount();

  protected:
    int_type overflow (int_type c = EOF) override;
    int_type pbackfail(int_type c = EOF) override;
    int_type underflow() override;
    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which = ios_base::in | ios_base::out) override;
    streambuf* setbuf(char* s, streamsize n) override;

  private:
     using strstate = T1;                      // exposition only

     static const strstate allocated;          // exposition only
     static const strstate constant;           // exposition only
     static const strstate dynamic;            // exposition only
     static const strstate frozen;             // exposition only
     strstate strmode;                         // exposition only
     streamsize alsize;                        // exposition only
     void* (*palloc)(size_t);                  // exposition only
     void (*pfree)(void*);                     // exposition only
  };
}

1 The class strstreambuf associates the input sequence, and possibly the output sequence, with an object of some character array type, whose elements store arbitrary values. The array object has several attributes.

2 [Note 1: For the sake of exposition, these are represented as elements of a bitmask type (indicated here as T1) called strstate. The elements are:]

3 [Note 2: For the sake of exposition, the maintained data is presented here as:]

4 Each object of class strstreambuf has a seekable area, delimited by the pointers seeklow and seekhigh. If gnext is a null pointer, the seekable area is undefined. Otherwise, seeklow equals gbeg and seekhigh is either pend, if pend is not a null pointer, or gend.

D.14.2.2 [depr.strstreambuf.cons] strstreambuf constructors

explicit strstreambuf(streamsize alsize_arg);

1 Effects: Initializes the base class with streambuf(). The postconditions of this function are indicated in Table 147.

Table 147: strstreambuf(streamsize) effects [tab:depr.strstreambuf.cons.sz]

2 Effects: Initializes the base class with streambuf(). The postconditions of this function are indicated in Table 148.

Table 148: strstreambuf(void* (*)(size_t), void (*)(void*)) effects

strstreambuf(char* gnext_arg, streamsize n, char* pbeg_arg = nullptr);
strstreambuf(signed char* gnext_arg, streamsize n,
             signed char* pbeg_arg = nullptr);
strstreambuf(unsigned char* gnext_arg, streamsize n,
             unsigned char* pbeg_arg = nullptr);

3 Effects: Initializes the base class with streambuf(). The postconditions of this function are indicated in Table 149.

Table 149: strstreambuf(charT*, streamsize, charT*) effects [tab:depr.strstreambuf.cons.ptr]

4 gnext_arg shall point to the first element of an array object whose number of elements N is determined as follows:

• If n > 0, N is n.
• If n == 0, N is std::strlen(gnext_arg).
• If n < 0, N is INT_MAX.¹

5 If pbeg_arg is a null pointer, the function executes:

   setg(gnext_arg, gnext_arg, gnext_arg + N);

6 Otherwise, the function executes:

   setg(gnext_arg, gnext_arg, pbeg_arg);
   setp(pbeg_arg,  pbeg_arg + N);

strstreambuf(const char* gnext_arg, streamsize n);
strstreambuf(const signed char* gnext_arg, streamsize n);
strstreambuf(const unsigned char* gnext_arg, streamsize n);

7 Effects: Behaves the same as strstreambuf((char*)gnext_arg,n), except that the constructor also sets constant in strmode.

virtual ~strstreambuf();

8 Effects: Destroys an object of class strstreambuf. The function frees the dynamically allocated array object only if (strmode & allocated) != 0 and (strmode & frozen) == 0. (D.14.2.4 [depr.strstreambuf.virtuals] describes how a dynamically allocated array object is freed.)

D.14.2.3 [depr.strstreambuf.members] Member functions

void freeze(bool freezefl = true);

1 Effects: If strmode & dynamic is nonzero, alters the freeze status of the dynamic array object as follows:

• If freezefl is true, the function sets frozen in strmode.
• Otherwise, it clears frozen in strmode.

char* str();

2 Effects: Calls freeze(), then returns the beginning pointer for the input sequence, gbeg.

3 Remarks: The return value can be a null pointer.

int pcount() const;

4 Effects: If the next pointer for the output sequence, pnext, is a null pointer, returns zero. Otherwise, returns the current effective length of the array object as the next pointer minus the beginning pointer for the output sequence, pnext - pbeg.

D.14.2.4 [depr.strstreambuf.virtuals] strstreambuf overridden virtual functions

int_type overflow(int_type c = EOF) override;

1 Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:

• If c != EOF and if either the output sequence has a write position available or the function makes a write position available (as described below), assigns c to *pnext++.
  Returns (unsigned char)c.
• If c == EOF, there is no character to append.
  Returns a value other than EOF.

2 Returns EOF to indicate failure.

3 Remarks: The function can alter the number of write positions available as a result of any call.

4 To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements n to hold the current array object (if any), plus at least one additional write position. How many additional write positions are made available is otherwise unspecified. If palloc is not a null pointer, the function calls (*palloc)(n) to allocate the new dynamic array object. Otherwise, it evaluates the expression new charT[n]. In either case, if the allocation fails, the function returns EOF. Otherwise, it sets allocated in strmode.

5 To free a previously existing dynamic array object whose first element address is p: If pfree is not a null pointer, the function calls (*pfree)(p). Otherwise, it evaluates the expression delete[]p.

6 If (strmode & dynamic) == 0, or if (strmode & frozen) != 0, the function cannot extend the array (reallocate it with greater length) to make a write position available.

7 Recommended practice: An implementation should consider alsize in making the decision how many additional write positions to make available.

int_type pbackfail(int_type c = EOF) override;

8 Puts back the character designated by c to the input sequence, if possible, in one of three ways:

• If c != EOF, if the input sequence has a putback position available, and if (char)c == gnext[-1], assigns gnext - 1 to gnext.
  Returns c.
• If c != EOF, if the input sequence has a putback position available, and if strmode & constant is zero, assigns c to *--gnext.
  Returns c.
• If c == EOF and if the input sequence has a putback position available, assigns gnext - 1 to gnext.
  Returns a value other than EOF.

9 Returns EOF to indicate failure.

10 Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen. The function can alter the number of putback positions available as a result of any call.

int_type underflow() override;

11 Effects: Reads a character from the input sequence, if possible, without moving the stream position past it, as follows:

• If the input sequence has a read position available, the function signals success by returning (unsigned char)*gnext.
• Otherwise, if the current write next pointer pnext is not a null pointer and is greater than the current read end pointer gend, makes a read position available by assigning to gend a value greater than gnext and no greater than pnext.
  Returns (unsigned char)*gnext.

12 Returns EOF to indicate failure.

13 Remarks: The function can alter the number of read positions available as a result of any call.

pos_type seekoff(off_type off, seekdir way, openmode which = in | out) override;

14 Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 150.

Table 150: seekoff positioning [tab:depr.strstreambuf.seekoff.pos]

15 For a sequence to be positioned, if its next pointer is a null pointer, the positioning operation fails. Otherwise, the function determines newoff as indicated in Table 151.

Table 151: newoff values [tab:depr.strstreambuf.seekoff.newoff]

16 If (newoff + off) < (seeklow - xbeg) or (seekhigh - xbeg) < (newoff + off), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.

17 Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).

pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;

18 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 & ios::in) != 0, positions the input sequence.
• If (which & ios::out) != 0, positions the output sequence.
• If the function positions neither sequence, the positioning operation fails.

19 For a sequence to be positioned, if its next pointer 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 (seekhigh - seeklow), the positioning operation fails
• Otherwise, the function adds newoff to the beginning pointer xbeg and store the result in the next pointer xnext.

20 Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).

streambuf<char>* setbuf(char* s, streamsize n) override;

21 Effects: Behavior is implementation-defined, except that setbuf(0, 0) has no effect.

D.14.3 [depr.istrstream] Class istrstream

D.14.3.1 [depr.istrstream.general] General

namespace std {
  class istrstream : public basic_istream<char> {
  public:
    explicit istrstream(const char* s);
    explicit istrstream(char* s);
    istrstream(const char* s, streamsize n);
    istrstream(char* s, streamsize n);
    virtual ~istrstream();
   
    strstreambuf* rdbuf() const;
    char* str();
  private:
    strstreambuf sb;            // exposition only
  };
}

1 The class istrstream supports the reading of objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• sb, the strstreambuf object.

D.14.3.2 [depr.istrstream.cons] istrstream constructors

explicit istrstream(const char* s);
explicit istrstream(char* s);

1 Effects: Initializes the base class with istream(&sb) and sb with strstreambuf(s, 0). s shall designate the first element of an NTBS.

istrstream(const char* s, streamsize n);
istrstream(char* s, streamsize n);

2 Effects: Initializes the base class with istream(&sb) and sb with strstreambuf(s,n). s shall designate the first element of an array whose length is n elements, and n shall be greater than zero.

D.14.3.3 [depr.istrstream.members] Member functions

strstreambuf* rdbuf() const;

1 Returns: const_cast<strstreambuf*>(&sb).

char* str();

2 Returns: rdbuf()->str().

D.14.4 [depr.ostrstream] Class ostrstream

D.14.4.1 [depr.ostrstream.general] General

namespace std {
  class ostrstream : public basic_ostream<char> {
  public:
    ostrstream();
    ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);
    virtual ~ostrstream();

    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    char* str();
    int pcount() const;

  private:
    strstreambuf sb;            // exposition only
  }; 
}

1 The class ostrstream supports the writing of objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• sb, the strstreambuf object.

D.14.4.2 [depr.ostrstream.cons] ostrstream constructors

ostrstream();

1 Effects: Initializes the base class with ostream(&sb) and sb with strstreambuf().

ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);

2 Effects: Initializes the base class with ostream(&sb), and sb with one of two constructors:

• If (mode & app) == 0, then s shall designate the first element of an array of n elements. The constructor is strstreambuf(s, n, s).
• If (mode & app) != 0, then s shall designate the first element of an array of n elements that contains an NTBS whose first element is designated by s. The constructor is strstreambuf(s, n, s + std::strlen(s)).²

D.14.4.3 [depr.ostrstream.members] Member functions

strstreambuf* rdbuf() const;

1 Returns: (strstreambuf*)&sb.

void freeze(bool freezefl = true);

2 Effects: Calls rdbuf()->freeze(freezefl).

char* str();

3 Returns: rdbuf()->str().

int pcount() const;

4 Returns: rdbuf()->pcount().

D.14.5 [depr.strstream] Class strstream

D.14.5.1 [depr.strstream.general] General

namespace std {
  class strstream
    : public basic_iostream<char> {
  public:
    // types
    using char_type = char;
    using int_type  = char_traits<char>::int_type;
    using pos_type  = char_traits<char>::pos_type;
    using off_type  = char_traits<char>::off_type;

    // constructors/destructor
    strstream();
    strstream(char* s, int n,
              ios_base::openmode mode = ios_base::in|ios_base::out);
    virtual ~strstream();

    // members
    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    int pcount() const;
    char* str();

  private:
    strstreambuf sb;            // exposition only
  };
}

1 The class strstream supports reading and writing from objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• sb, the strstreambuf object.

D.14.5.2 [depr.strstream.cons] strstream constructors

strstream();

1 Effects: Initializes the base class with iostream(&sb).

strstream(char* s, int n,
           ios_base::openmode mode = ios_base::in|ios_base::out);

2 Effects: Initializes the base class with iostream(&sb), and sb with one of the two constructors:

• If (mode & app) == 0, then s shall designate the first element of an array of n elements. The constructor is strstreambuf(s,n,s).
• If (mode & app) != 0, then s shall designate the first element of an array of n elements that contains an NTBS whose first element is designated by s. The constructor is strstreambuf(s,n,s+ std::strlen(s)).

D.14.5.3 [depr.strstream.dest] strstream destructor

virtual ~strstream();

1 Effects: Destroys an object of class strstream.

D.14.5.4 [depr.strstream.oper] strstream operations

strstreambuf* rdbuf() const;

1 Returns: const_cast<strstreambuf*>(&sb).

void freeze(bool freezefl = true);

2 Effects: Calls rdbuf()->freeze(freezefl).

char* str();

3 Returns: rdbuf()->str().

int pcount() const;

4 Returns: rdbuf()->pcount().