std::strstream::strstream(3)

NAME
std::strstream::strstream - std::strstream::strstream

Synopsis
   strstream(); (1) (deprecated in C++98)
                        (removed in C++26)
   strstream( char* s, int n, std::ios_base::openmode mode = (deprecated in C++98)
                        std::ios_base::in | (2) (removed in C++26)
   std::ios_base::out );
   Constructs new input/output strstream and its underlying std::strstreambuf.
   1) Default-constructs the underlying std::strstreambuf, which creates a dynamically
   growing buffer, and initializes the base class with the address of the strstreambuf
   member.
   2) Initialized the base class with the address of the underlying std::strstreambuf
   member, which is initialized in one of the two possible ways, both of which use a
   user-provided fixed-size array:
   a) if (mode & app) == 0 (the app bit is not set in mode), constructs the buffer by
   calling strstreambuf(s, n, s). The behavior is undefined if there are less than n
   elements in the array whose first element is pointed to by s.
   b) if (mode & app) != 0 (the app bit is set in mode), constructs the buffer by
   calling strstreambuf(s, n, s + std::strlen(s)). The behavior is undefined if there
   are less than n elements in the array whose first element is pointed to by s or if
   the array does not contain a valid null-terminated character sequence.

Parameters
   s - char array to use as the output buffer
   n - size of the array to be used for output
          specifies stream open mode. It is a bitmask type, the following constants are
          defined (although only app is used):
          Constant Explanation
          app seek to the end of stream before each write
   mode - binary open in binary mode
          in open for reading
          out open for writing
          trunc discard the contents of the stream when opening
          ate seek to the end of stream immediately after open
          noreplace (C++23) open in exclusive mode

Example
// Run this code
 #include <iostream>
 #include <string>
 #include <strstream>
 int main()
 {
     // dynamic buffer
     std::strstream s1;
     s1 << 1 << ' ' << 3.14 << " example" << std::ends;
     std::cout << "Buffer holds: '" << s1.str() << "'\n";
     s1.freeze(false);
     int n;
     double d;
     std::string w;
     s1 >> n >> d >> w;
     std::cout << "Read back: n = " << n
               << ", d = " << d
               << ", w = '" << w << "'\n";
     // static buffer
     char arr[20] = "-1 -3.14 ";
     std::strstream s2(arr, sizeof arr, std::ios_base::app);
     s2 << "another" << std::ends;
     std::cout << "Buffer holds: '" << s2.str() << "'\n";
     s2 >> n >> d >> w;
     std::cout << "Read back: n = " << n
               << ", d = " << d
               << ", w = '" << w << "'\n";
 }

Output:
 Buffer holds: '1 3.14 example'
 Read back: n = 1, d = 3.14, w = 'example'
 Buffer holds: '-1 -3.14 another'
 Read back: n = -1, d = -3.14, w = 'another'
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
                      overload (2) only considered the case considers cases (mode &
   LWG 115 C++98 mode & app == 0 (== has higher precedence app) == 0
                      than &) and (mode & app) != 0

See also
   constructor constructs a strstreambuf object
                 (public member function of std::strstreambuf)
   constructor constructs an istrstream object, optionally allocating the buffer
                 (public member function of std::istrstream)
   constructor constructs an ostrstream object, optionally allocating the buffer
                 (public member function of std::ostrstream)