fwopen — open a
(See libbsd(7) for include usage.)
void *cookie, int
(*readfn)(void *, char *, int),
int (*writefn)(void *, const
char *, int), off_t
(*seekfn)(void *, off_t, int),
(*readfn)(void *, char *, int));
(*writefn)(void *, const char *, int));
function associates a stream with up to four “I/O
readfn or writefn must be
specified; the others can be given as an appropriately-typed
NULL pointer. These I/O 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
seekfn and closefn must match
those, respectively, of read(2),
write(2), lseek(2), and
close(2) with the single exception that they are passed
the cookie argument specified to
in place of the traditional file descriptor argument.
Read and write I/O functions are allowed to change the underlying buffer on fully buffered or line buffered streams by calling setvbuf(3). 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.
All user I/O functions can report an error by returning -1. Additionally, all of the functions should set the external variable errno appropriately if an error occurs.
An error on
does not keep the stream open.
Upon successful completion,
FILE pointer. Otherwise,
NULL is returned and the global variable
errno is set to indicate the error.
funopen() functions first appeared in
funopen() function may not be portable
to systems other than BSD.
OpenBSD and DragonFly the
funopen() interface erroneously assumes that
fpos_t is an integral type, and uses it in the
seekfn hook; but because code using a
seekfn hook will fail to build on systems where
fpos_t is a struct, and it will need to be slightly
fixed anyway, the implementation provided by libbsd (in the same way as
NetBSD) uses the correct off_t
|March 19, 2004||Debian|