I'm thinking it might be helpful in the discussion for me to try to document in precise terms what asio would need from error_code and how it would be used. What's needed from error_code ============================= Testing for equality: Given error_code ec1(value1, category1); error_code ec2(value1, category1); error_code ec3(value2, category1); Then ec1 == ec2 evaluates to true ec1 == ec3 evaluates to false What asio will say ================== (For the sake of brevity I will only discuss a couple of error codes, but others will follow the same pattern.) There will be an error_code object: namespace boost { namespace asio { namespace error { extern error_code connection_reset; }}} On non-POSIX implementations, the initialisation of connection_reset is implementation-defined. On POSIX implementations, the initialisation of connection_reset shall be: error_code connection_reset(ECONNRESET, from_errno); such that both of the following expressions shall evaluate to true: connection_reset == error_code(ECONNRESET, from_errno) connection_reset.errno_value() == ECONNRESET In the following code, sock is a variable with the type boost::asio::ip::tcp::socket. char buf[128]; error_code ec; sock.receive(boost::asio::buffer(buf), ec); If an error occurs during the socket receive() such that the connection was reset by the peer (and this condition is reported to asio by a unique system error code), the following expression shall evaluate to true on all implementations (POSIX and non-POSIX): ec == boost::asio::error::connection_reset Furthermore, on POSIX implementations the following expressions shall evaluate to true: ec == error_code(ECONNRESET, from_errno) ec.errno_value() == ECONNRESET There will be an error_code object: namespace boost { namespace asio { namespace error { extern error_code name_not_found; }}} On non-POSIX implementations, the initialisation of name_not_found is implementation-defined. On POSIX implementations, the initialisation of name_not_found shall be: ??? // Needs error category support. From // the getaddrinfo error EAI_NONAME. In the following code, resolver is a variable with the type boost::asio::ip::tcp::resolver. boost::asio::ip::tcp::resolver::query query("foo", "bar"); error_code ec; resolver.resolve(query, ec); If an error occurs during name resolution such that the host is not found, the following expression shall evaluate to true on all implementations (POSIX and non-POSIX): ec == boost::asio::error::name_not_found Furthermore, on POSIX implementations the following expressions shall evaluate to true: ??? // Again, needs error category support. That's all I can think of for now. Cheers, Chris