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

std::ostrstream::ostrstream: std::ostrstream::ostrstream

NAME

std::ostrstream::ostrstream - std::ostrstream::ostrstream

Synopsis

ostrstream(); (1)
ostrstream(char* s, int n, std::ios_base::openmode mode = std::ios_base::out); (2)

Constructs new 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 write to 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 as the output buffer
       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>

  int main()
  {
      std::ostrstream s1; // dynamic buffer
      s1 << 1 << ' ' << 3.14 << " example\n" << std::ends;
      std::cout << s1.str();
      s1.freeze(false);

      char arr[15] = "Hello";

      std::ostrstream s2(arr, sizeof arr, std::ios_base::app);
      s2 << ", world!" << std::ends;
      std::cout << s2.str() << '\n';
      std::cout << arr << '\n'; // streams use the provided arrays
  }

Output:

  1 3.14 example
  Hello, world!
  Hello, world!