Description GIOStream represents an object that has both read and write streams. Generally the two streams acts as separate input and output streams, but they share some common resources and state. For instance, for seekable streams they may use the same position in both streams. Examples of GIOStream objects are GSocketConnection which represents a two-way network connection, and GFileIOStream which represent a file handle opened in read-write mode. To do the actual reading and writing you need to get the substreams with g_io_stream_get_input_stream() and g_io_stream_get_output_stream(). The GIOStream object owns the input and the output streams, not the other way around, so keeping the substreams alive will not keep the GIOStream object alive. If the GIOStream object is freed it will be closed, thus closing the substream, so even if the substreams stay alive they will always just return a G_IO_ERROR_CLOSED for all operations. To close a stream use g_io_stream_close() which will close the common stream object and also the individual substreams. You can also close the substreams themselves. In most cases this only marks the substream as closed, so further I/O on it fails. However, some streams may support "half-closed" states where one direction of the stream is actually shut down.