Asio includes classes added to permit synchronous and asynchronous read and write operations to be performed on POSIX file descriptors, such as pipes, standard input and output, and various devices.
These classes also provide limited support for regular files. This support
assumes that the underlying read and write operations provided by the operating
system never fail with
EWOULDBLOCK. (This assumption
normally holds for buffered file I/O.) Synchronous and asynchronous read
and write operations on file descriptors will succeed but the I/O will
always be performed immediately. Wait operations, and operations involving
asio::null_buffers, are not portably supported.
For example, to perform read and write operations on standard input and output, the following objects may be created:
posix::stream_descriptor in(my_io_context, ::dup(STDIN_FILENO)); posix::stream_descriptor out(my_io_context, ::dup(STDOUT_FILENO));
These are then used as synchronous or asynchronous read and write streams. This means the objects can be used with any of the read(), async_read(), write(), async_write(), read_until() or async_read_until() free functions.
POSIX stream descriptors are only available at compile time if supported
by the target operating system. A program may test for the macro
ASIO_HAS_POSIX_STREAM_DESCRIPTOR to determine
whether they are supported.