< cpp‎ | io‎ | ostrstream

char* str();

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


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.



Return value

Pointer to the beginning of the buffer in the associated std::strsteambuf or NULL if no buffer is available.


#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";

Possible output:

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

See also

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