ostrstream

class ostrstream : public ostream {
public:
    ostrstream();
    ostrstream(char *s, streamsize n,
        ios_base::openmode mode = ios_base::out);
    strstreambuf *rdbuf() const;
    void freeze(bool frz = true);
    char *str();
    streamsize pcount() const;
    };

The class describes an object that controls insertion of elements and encoded objects into a stream buffer of class strstreambuf. The object stores an object of class strstreambuf.