associates a stream with up to four
must be specified;
the others can be given as an appropriately-typed
functions will be used to read, write, seek and
close the new stream.
In general, omitting a function means that any attempt to perform the
associated operation on the resulting stream will fail.
If the close function is omitted, closing the stream will flush
any buffered output and then succeed.
The calling conventions of
must match those, respectively, of
with the single exception that they are passed the
argument specified to
in place of the traditional file descriptor argument.
Read and write
functions are allowed to change the underlying buffer
on fully buffered or line buffered streams by calling
They are also not required to completely fill or empty the buffer.
They are not, however, allowed to change streams from unbuffered to buffered
or to change the state of the line buffering flag.
They must also be prepared to have read or write calls occur on buffers other
than the one most recently specified.
functions can report an error by returning -1.
Additionally, all of the functions should set the external variable
appropriately if an error occurs.
An error on
does not keep the stream open.
As a convenience, the include file
defines the macros
as calls to
with only a read or write function specified.