std::ostream interface to an OLE IStream
- by PaulH
I have a Visual Studio 2008 C++ application using IStreams. I would like to use the IStream connection in a std::ostream. Something like this:
IStream* stream = /*create valid IStream instance...*/;
IStreamBuf< WIN32_FIND_DATA > sb( stream );
std::ostream os( &sb );
WIN32_FIND_DATA d = { 0 };
// send the structure along the IStream
os << d;
To accomplish this, I've implemented the following code:
template< class _CharT, class _Traits >
inline std::basic_ostream< _CharT, _Traits >&
operator<<( std::basic_ostream< _CharT, _Traits >& os, const WIN32_FIND_DATA& i )
{
const _CharT* c = reinterpret_cast< const _CharT* >( &i );
const _CharT* const end = c + sizeof( WIN32_FIND_DATA ) / sizeof( _CharT );
for( c; c < end; ++c ) os << *c;
return os;
}
template< typename T >
class IStreamBuf : public std::streambuf
{
public:
IStreamBuf( IStream* stream ) : stream_( stream )
{
setp( reinterpret_cast< char* >( &buffer_ ),
reinterpret_cast< char* >( &buffer_ ) + sizeof( buffer_ ) );
};
virtual ~IStreamBuf()
{
sync();
};
protected:
traits_type::int_type FlushBuffer()
{
int bytes = std::min< int >( pptr() - pbase(), sizeof( buffer_ ) );
DWORD written = 0;
HRESULT hr = stream_->Write( &buffer_, bytes, &written );
if( FAILED( hr ) )
{
return traits_type::eof();
}
pbump( -bytes );
return bytes;
};
virtual int sync()
{
if( FlushBuffer() == traits_type::eof() )
return -1;
return 0;
};
traits_type::int_type overflow( traits_type::int_type ch )
{
if( FlushBuffer() == traits_type::eof() )
return traits_type::eof();
if( ch != traits_type::eof() )
{
*pptr() = ch;
pbump( 1 );
}
return ch;
};
private:
/// data queued up to be sent
T buffer_;
/// output stream
IStream* stream_;
}; // class IStreamBuf
Yes, the code compiles and seems to work, but I've not had the pleasure of implementing a std::streambuf before. So, I'd just like to know if it's correct and complete.
Thanks,
PaulH
