FUNOPEN(3) | Library Functions Manual | FUNOPEN(3) |
funopen
, funopen2
,
fropen
, fropen2
,
fwopen
, fwopen2
—
#include <stdio.h>
FILE *
funopen
(void *cookie,
int (*readfn)(void *, char *, int),
int (*writefn)(void *, const char *, int),
off_t (*seekfn)(void *, off_t, int),
int (*closefn)(void *));
FILE *
funopen2
(void *cookie,
ssize_t (*readfn)(void *, void *, size_t),
ssize_t (*writefn)(void *, const void *, size_t),
off_t (*seekfn)(void *, off_t, int),
int (*flushfn)(void *), int
(*closefn)(void *));
FILE *
fropen
(void
*cookie, int
(*readfn)(void *, char *, int));
FILE *
fropen2
(void
*cookie, ssize_t
(*readfn)(void *, void *, size_t));
FILE *
fwopen
(void
*cookie, int
(*writefn)(void *, const char *, int));
FILE *
fwopen2
(void
*cookie, ssize_t
(*writefn)(void *, const void *, size_t));
funopen
() function associates a stream with up to
four “I/O functions”. Either
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.
The funopen2
() function provides sightly
different read and write signatures, which match the corresponding system
calls better, plus the ability to augment the stream's default flushing
function. If a flushing function is provided, it is called after all data
has been written to the 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 readfn,
writefn, seekfn and
closefn must match those, respectively, of
read(2),
write(2),
lseek(2), and
close(2); except that they are
passed the cookie argument specified to
funopen
() 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 closefn does not keep the stream open.
As a convenience, the include file
<stdio.h>
defines the macros
fropen
() and fwopen
() as
calls to funopen
() with only a read or write
function specified.
funopen
() returns a
FILE
pointer. Otherwise, NULL
is returned and the global variable errno is set to
indicate the error.
funopen
() functions first appeared in
4.4BSD. The funopen2
()
functions first appeared in NetBSD 7.0.
March 16, 2012 | NetBSD 9.0 |