When available, Asio can use the std::error_code and std::system_error classes for reporting errors. In this case, the names asio::error_code and asio::system_error will be typedefs for these standard classes.

System error support is automatically enabled for g++ 4.6 and later, when the -std=c++0x or -std=gnu++0x compiler options are used. It may be disabled by defining ASIO_DISABLE_STD_SYSTEM_ERROR, or explicitly enabled for other compilers by defining ASIO_HAS_STD_SYSTEM_ERROR.