Hi Scott, me22 <me22.ca@gmail.com> wrote:
From http://asio.sourceforge.net/boost_asio_0_3_7/libs/ asio/doc/examples/httpclient_sync_client_cpp.html :
boost::asio::streambuf request; std::ostream request_stream(&request); request_stream << "GET " << argv[2] << " HTTP/1.0\r\n"; request_stream << "Host: " << argv[1] << "\r\n"; request_stream << "Accept: */*\r\n"; request_stream << "Connection: close\r\n\r\n";
// Send the request. boost::asio::write(socket, request);
What advantage is the boost::asio::streambuf providing here? I don't see a different between it and just using a stringstream and sending the .str().
For writing data, the main advantage over stringstream (or strstream) that I see is that data copying can be minimised. I've tried to keep the interface such that internal buffers can be allocated separately and chained deque-style. Using a chain of buffers, data can be appended to the end or extracted from the front without needing to copy around the existing contents. However, if there's a single contiguous buffer then every time the buffer is resized there's the possibility that all data in the buffer would have to be copied to a new location. Note that the current implementation of asio::streambuf does use a contiguous buffer so I could implement it quickly :) So at the moment this particular benefit isn't realised. I don't know whether the standard permits a stringstream using non-contiguous buffers. 27.7.1.3/8 at least seems to promote using a single character array. However, even if it is permitted... Depending on your std::string and std::stringstream implementation, you will probably incur an additional memory allocation and data copy when you call .str() on the stringstream to extract the contents. Calling asio::write() on an asio::streambuf is guaranteed to write directly from the internal buffers. Cheers, Chris