NAME
funopen,
funopen2,
fropen,
fropen2,
fwopen,
fwopen2
—
open a stream
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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
*));
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));
DESCRIPTION
The
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.
RETURN VALUES
Upon successful completion,
funopen() returns a
FILE
pointer. Otherwise,
NULL
is returned and the global variable
errno is set to
indicate the error.
ERRORS
-
-
- [
EINVAL
]
- The funopen() function was called without
either a read or write function. The funopen() function
may also fail and set errno for any of the errors
specified for the routine
malloc(3).
SEE ALSO
fcntl(2),
open(2),
fclose(3),
fmemopen(3),
fopen(3),
fseek(3),
setbuf(3)
HISTORY
The
funopen() functions first appeared in
4.4BSD. The
funopen2() functions
first appeared in
NetBSD 7.0.
CAVEATS
All three functions are specific to
NetBSD and thus
unportable.