Hi Dmitry, Dmitry Smirnov wrote:
Hi, Ion!
It seems I found the difference between "resize" and "reserve"
After changing resize to reserve in following code m_objSendVectorStream.tellp() will return -1 instead of size of data packet :-(
m_objSendVectorStream.resize( QueueSettings::maxMessageSize() );
m_objSendVectorStream.seekp( 0 ); { boost::archive::defOArchive objOArchive( m_objSendVectorStream ); objOArchive << objData; }
In theory, "reserve()" means "reserve memory to avoid reallocations" but does _not_ insert characters in the stream, so the stream size will be zero. I mean: -> "resize(resize_size)" called "resize(resize_size)" in the underlying vector, so vector was zero-filled (vector.size() == resize_size) and thus, the result was that '0' characters were introduced in the stream and the position was reset to 0. ->"reserve(reserve_size)" calls "reserve(reserve_size)" in the vector, so memory is allocated but no characters are introduced in the vector (vector.size() == 0), and the position is reset to zero, so you would be in the end of the stream (position 0 == eof since there are no characters). The formatted stream is unchanged but you guarantee no allocations. So: basic_vectorstream<...> vstream; vstream.resize(1000); was equivalent to inserting 1000 '0' characters in the stream and to reset the position. I wanted to avoid this, because the only way to write to the stream should be though stream functions. basic_vectorstream<...> vstream; vstream.reserve(1000); should be equivalent to just creating the vectorstream (so there are no characters in the stream). I need to investigate if tellp returning -1 in this case is correct (should it return 0 or eof?) My intention was to make this equivalent to creating a file.: std::fstream file("file, std::ios_base::in | std::ios_base::out); file.tellp() == ? Hmmm,you were just telling me what the difference is or you consider this a bug? Regards, Ion