Serializing data in std :: streambuf

Question

I have a Visual Studio 2008 C ++ project where I am trying to serialize data from several classes into a custom implementation of std::streambuf .

Data classes with their serialization:

 struct Header { /*...*/ }; inline std::ostream& operator<<( std::ostream& os, const Header& h ) { /* serialize the members of Header here */ os.write( h.some_member, sizeof( h.some_member ) ); return os; } struct Info { /*...*/ }; inline std::ostream& operator<<( std::ostream& os, const Info& i ) { /* serialize the members of Info here */ return os; } 

The streambuffer implementation provides buffered I / O and overrides underflow and overflow .

 class MyStreamBuf : public std::streambuf { public: MyStreamBuf() { InitBuffers(); }; private: void InitBuffers() { recv_buffer_.resize( buff_size ); send_buffer_.resize( buff_size ); setg( &recv_buffer_[ 0 ], &recv_buffer_[ 0 ], &recv_buffer_[ 0 ] ); setp( &send_buffer_[ 0 ], &send_buffer_[ 0 ] ); }; enum { buff_size = 512 }; std::vector< char_type > recv_buffer_; std::vector< char_type > send_buffer_; int_type underflow() { /* ... */ }; int_type overflow( char_type c ) { *pptr() = c; pbump( 1 ); // if the buffer is full, flush the data if( pptr() == epptr() ) flush(); return c; }; void flush() { std::ptrdiff_t n = pptr() - pbase(); int written = /* send n bytes to the data destination */ pbump( -written ); }; }; // class MyStreamBuf 

My destiny is something like this:

 Header h( /* some useful info */ ); Info i( /* some useful info */ ); MyStreamBuf dest; std::iostream my_stream( &dest ); dest << h << i; // MyStreambuf::overflow() is never called! 

But MyStreambuf::overflow never called. What do I need to do to get data in my buffer?

Thanks PaulH

Answer 1

You need to call flush() on iostream (or call pubsync() on your streambuf).

Traditionally, you do this in the destructor of your streambuf (just like destructor filebuf calls close() ), in which case you just need to destroy it.

It is also common to provide a class that inherits from iostream, which owns an instance of your streambuf and guarantees its redness / destruction when necessary.