NAME¶
funopen
,
fropen
,
fwopen
—
open a stream
LIBRARY¶
library “libbsd”
SYNOPSIS¶
#include
<bsd/stdio.h>
FILE *
funopen
(
const
void *cookie,
int (*readfn)(void *,
char *, int),
int (*writefn)(void *,
const char *, int),
off_t (*seekfn)(void
*, off_t, int),
int (*closefn)(void
*));
FILE *
fropen
(
void
*cookie,
int
(*readfn)(void *, char *, int));
FILE *
fwopen
(
void
*cookie,
int
(*writefn)(void *, const char *, int));
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.
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) with the single exception 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),
fopen(3),
fseek(3),
setbuf(3)
HISTORY¶
The
funopen
() functions first appeared in
4.4BSD.
BUGS¶
The
funopen
() function may not be portable to
systems other than
BSD.
On
FreeBSD,
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 types.