std::ostrstream::str(3)

NAME
std::ostrstream::str - std::ostrstream::str

Synopsis
   char* str();
   Returns the pointer to the beginning of the buffer, after freezing it. Effectively
   calls rdbuf()->str()

Parameters
   (none)

Return value
   Pointer to the beginning of the buffer in the associated std::strsteambuf or a null
   pointer if no buffer is available.

Notes
   Before a call to str() that uses the result as a C string, the stream buffer must be
   null-terminated. Regular output such as with stream << 1.2 does not store a null
   terminator, it must be appended explicitly, typically with the manipulator
   std::ends.
   After a call to str(), dynamic streams become frozen. A call to freeze(false) is
   required before exiting the scope in which this ostrstream object was created.
   otherwise the destructor will leak memory. Also, additional output to a frozen
   stream may be truncated once it reaches the end of the allocated buffer, which may
   leave the buffer not null-terminated.

Example
// Run this code
 #include <strstream>
 #include <iostream>
 int main()
 {
     std::ostrstream dyn; // dynamically-allocated output buffer
     dyn << "Test: " << 1.23; // not adding std::ends to demonstrate append behavior
     std::cout << "The output stream holds \"";
     std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
     // the stream is now frozen due to str()
     dyn << " More text" << std::ends;
     std::cout << "The output stream holds \"";
     std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
     dyn.freeze(false);
 }

Possible output:
 The stream holds "Test: 1.23"
 The stream holds "Test: 1.23 More "

See also
   str marks the buffer frozen and returns the beginning pointer of the input sequence
       (public member function of std::strstreambuf)