std::strstream::strstream (3) - Linux Manuals

std::strstream::strstream: std::strstream::strstream

NAME

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

Synopsis

strstream(); (1)
strstream(char* s, int n, std::ios_base::openmode mode (2)
= std::ios_base::in | 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 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 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

Example

// Run this code

  #include <iostream>
  #include <strstream>
  #include <string>

  int main()
  {
      // dynamic buffer
      std::strstream s1; // dynamic buffer
      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'