FUNOPEN(3) | Library Functions Manual | FUNOPEN(3) |
funopen
, fropen
,
fwopen
— open a
stream
Standard C Library (libc, -lc)
#include
<stdio.h>
FILE *
funopen
(const
void *cookie, int
(*readfn)(void *, char *, int),
int (*writefn)(void *, const
char *, int), fpos_t
(*seekfn)(void *, fpos_t, int),
int (*closefn)(void
*));
FILE *
fropen
(void
*cookie, int
(*readfn)(void *, char *, int));
FILE *
fwopen
(void
*cookie, int
(*writefn)(void *, const char *, int));
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.
Upon successful completion, funopen
()
returns a FILE
pointer. Otherwise,
NULL
is returned and the global variable
errno is set to indicate the error.
The funopen
() functions first appeared in
4.4BSD.
The funopen
() function may not be portable
to systems other than BSD.
The funopen
() interface erroneously
assumes that fpos_t is an integral type; see
fseek(3) for a discussion of this
issue.
March 19, 2004 | macOS 14.6 |