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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     basic_stringbuf

      - Associates the input or output sequence with  a  sequence
     of arbitrary characters.



SYNOPSIS
     #include <sstream>
     template<class charT, class traits = char_traits<charT>,
             class Allocator = allocator<charT> >
     class basic_stringbuf
     : public basic_streambuf<charT, traits>



DESCRIPTION
     The class basic_stringbuf is derived  from  basic_streambuf.
     Its  purpose  is  to  associate the input or output sequence
     with a sequence of arbitrary characters. The sequence can be
     initialized  from,  or made available as, an object of class
     basic_string.       Each        object        of        type
     basic_stringbuf<charT,_traits,Allocator>  controls two char-
     acter sequences:



     o    A character input sequence;

     o    A character output sequence.


     Note: see basic_streambuf.

     The two sequences are related to each other, but are manipu-
     lated  separately. This allows you to read and write charac-
     ters   at   different   positions   in   objects   of   type
     basic_stringbuf_without  any  conflict  (as  opposed  to the
     basic_filebuf_objects, in which a  joint  file  position  is
     maintained).



INTERFACE
     template<class charT, class traits = char_traits<charT>,
             class allocator<charT> >
     class basic_stringbuf
     : public basic_streambuf<charT, traits> {

      public:

       typedef charT                        char_type;
       typedef typename traits::int_type    int_type;
       typedef typename traits::pos_type    pos_type;
       typedef typename traits::off_type    off_type;

       typedef basic_ios<charT, traits>     ios_type;
       typedef basic_string<charT, traits,
                            Allocator>      string_type;


       explicit basic_stringbuf(ios_base::openmode which =
                                 (ios_base::in | ios_base::out));

       explicit basic_stringbuf(const string_type& str,
                                ios_base::openmode which =
                                 (ios_base::in | ios_base::out));

       virtual ~basic_stringbuf();

       string_type str() const;
       void str(const string_type& str_arg);

     protected:

       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 streamsize xsputn(const char_type* s,
                                 streamsize n);

     };

TYPES
     char_type


        The type char_type is a synonym for the template  parame-
        ter charT.



     ios_type


        The type ios_type is an instantiation of class  basic_ios
        on type charT.



     off_type


        The type off_type is a synonym of type traits::off_type.



     pos_type


        The type pos_type is a synonym of type traits::pos_type.



     string_type


        The  type  string_type  is  an  instantiation  of   class
        basic_string on type charT.



     stringbuf


        The  type  stringbuf  is  an   instantiation   of   class
        basic_stringbuf on type char:

        typedef basic_stringbuf<char> stringbuf;



     traits_type


        The type traits_type is a synonym for the template param-
        eter traits.



     wstringbuf


        The  type  wstringbuf  is  an  instantiation   of   class
        basic_stringbuf on type wchar_t:

        typedef basic_stringbuf<wchar_t> wstringbuf;



CONSTRUCTORS
     explicit basic_stringbuf(ios_base::openmode which =
                    ios_base::in | ios_base::out);


        Constructs an object of class basic_stringbuf, initializ-
        ing the base class with basic_streambuf(), and initializ-
        ing the open mode with which.



     explicit basic_stringbuf(const string_type& str,
                    ios_base::openmode which =
                    ios_base::in | ios_base::out);


        Constructs an object of class basic_stringbuf, initializ-
        ing the base class with basic_streambuf(), and initializ-
        ing the open mode with which. The string  object  str  is
        copied  to  the underlying buffer. If the opening mode is
        in, initializes the input sequence to point to the  first
        character  of  the buffer. If the opening mode is out, it
        initializes the output sequence to  point  to  the  first
        character  of  the  buffer.  If the opening mode is out |
        app, it initializes the output sequence to point  to  the
        last character of the buffer.



DESTRUCTORS
     virtual ~basic_stringbuf();


        Destroys an object of class basic_stringbuf.



MEMBER FUNCTIONS
     int_type
     overflow(int_type c = traits::eof() );


        If the output sequence has a put position available,  and
        c  is not traits::eof(), then this function writes c into
        it. If there  is  no  position  available,  the  function
        increases  the  size  of  the  buffer  by allocating more
        memory and then writes c at the new current put position.
        If    the   operation   fails,   the   function   returns
        traits::eof(). Otherwise it returns traits::not_eof(c).



     int_type
     pbackfail( int_type c = traits::eof() );


        Puts back the character designated by c  into  the  input
        sequence. If traits::eq_int_type(c,traits::eof()) returns
        true, the function moves the input sequence one  position
        backward.  If  the  operation fails, the function returns
        traits::eof(). Otherwise it returns traits::not_eof(c).



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


        If the open mode is in | out, this  function  alters  the
        stream   position  of  both  the  input  and  the  output
        sequences. If the open mode is in, it alters  the  stream
        position of only the input sequence, and if it is out, it
        alters the stream position of the  output  sequence.  The
        new  position  is calculated by combining the two parame-
        ters off (displacement) and way (reference point). If the
        current  position of the sequence is invalid before repo-
        sitioning, the operation fails and the  return  value  is
        pos_type(off_type(-1)).  Otherwise  the  function returns
        the current new position.


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


        If the open mode is in | out, seekpos() alters the stream
        position  of  both the input and the output sequences. If
        the open mode is in, it alters the stream position of the
        input  sequence  only,  and  if  the open mode is out, it
        alters the stream position of the output  sequence  only.
        If the current position of the sequence is invalid before
        repositioning, the operation fails and the  return  value
        is pos_type(off_type(-1)). Otherwise the function returns
        the current new position.



     basic_streambuf<charT,traits>*
     setbuf(char_type*s, streamsize n);


        A stringbuf maintains an underlying character  array  for
        storing  buffered  characters.  This function gives you a
        way to resize or replace that buffer, with  certain  res-
        trictions.

        First of all, n must be greater than the number of  char-
        acters  currently in the buffer.  If n is too small, then
        setbuf has no effect and returns a null pointer to  indi-
        cate failure.

        If n is large enough, then this function has one  of  two
        effects:



             -    If s is not a null pointer, then setbuf  copies
                  the buffered contents of the stringbuf into the
                  n character array starting at s and installs  s
                  as  the  underlying character array used by the
                  stringbuf.   s  replaces  the  old   underlying
                  array.  In this case, the function returns s on
                  success or a null pointer to indicate failure.

                  Note that the stringbuf now owns s and  deletes
                  it  if  a subsequent call to setbuf replaces it
                  or, failing that, when the  stringbuf  is  des-
                  troyed.   A  program should not itself delete a
                  pointer passed to setbuf if the call  succeeds.
                  And  s  must  have been allocated from the heap
                  using new.

             -    If s is a null pointer, then setbuf resizes the
                  underlying  character  array  to  n characters.
                  The function returns a pointer to the beginning
                  of  the  resized array if the operation is suc-
                  cessful, or a null pointer if not.



     string_type
     str() const;


        Returns a string object of type string_type whose content
        is a copy of the underlying buffer contents.



     void
     str(const string_type& str_arg);


        Clears the underlying buffer and copies the string object
        str_arg  into  it. If the opening mode is in, initializes
        the input sequence to point to the first character of the
        buffer. If the opening mode is out, the function initial-
        izes the output sequence to point to the first  character
        of  the buffer. If the opening mode is out | app, it ini-
        tializes the output sequence to point to the last charac-
        ter of the buffer.



     int_type
     underflow();


        If the input sequence has a read position available,  the
        function returns the contents of this position. Otherwise
        it tries to expand the input sequence to match the output
        sequence,  and if possible returns the content of the new
        current position. The function returns  traits::eof()  to
        indicate failure.



     streamsize
     xsputn(const char_type* s, streamsize n);


        Writes up to n characters to  the  output  sequence.  The
        characters  written are obtained from successive elements
        of the array whose first element is designated by s.  The
        function returns the number of characters written.



EXAMPLE
     // stdlib/examples/manual/stringbuf.cpp
     //
     #include<iostream>
     #include<sstream>
     #include<string>

     void main ( )
     {
      using namespace std;

       // create a read/write string-stream object on tiny char
       // and attach it to an ostringstream object
      ostringstream out_1(ios_base::in | ios_base::out);

       // tie the istream object to the ostringstream object
      istream in_1(out_1.rdbuf());

       // output to out_1
      out_1 << "Here is the first output";

       // create a string object on tiny char
      string string_ex("l'heure est grave !");

       // open a read only string-stream object on tiny char
       // and initialize it
      istringstream in_2(string_ex);

       // output in_1 to the standard output
      cout << in_1.str() << endl;

       // output in_2 to the standard output
      cout << in_2.rdbuf() << endl;

       // reposition in_2 at the beginning
      in_2.seekg(0);

      stringbuf::pos_type pos;

       // get the current put position
       // equivalent to
       // out_1.tellp();
      pos = out_1.rdbuf()->pubseekoff(0,ios_base::cur,
                                      ios_base::out);

       // append the content of stringbuffer
       // pointed to by in_2 to the one
       // pointed to by out_1
      out_1 << ' ' << in_2.rdbuf();

       // output in_1 to the standard output
      cout << in_1.str() << endl;

       // position the get sequence
       // equivalent to
       // in_1.seekg(pos);
      in_1.rdbuf()->pubseekpos(pos, ios_base::in);

       // output "l'heure est grave !"
      cout << in_1.rdbuf() << endl << endl;
     }



SEE ALSO
     char_traits(3C++),     ios_base(3C++),      basic_ios(3C++),
     basic_streambuf(3C++),                   basic_string(3C++),
     basic_istringstream(3C++),        basic_ostringstream(3C++),
     basic_stringstream(3C++)

     Working Paper for Draft Proposed International Standard  for
     Information   Systems--Programming   Language  C++,  Section
     27.7.1



STANDARDS CONFORMANCE
     ANSI X3J16/ISO WG21 Joint C++ Committee

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