FreeBSD manual
download PDF document: fopencookie.3.pdf
FOPENCOOKIE(3) FreeBSD Library Functions Manual FOPENCOOKIE(3)
NAME
fopencookie - open a stream
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
typedef ssize_t
(*cookie_read_function_t)(void *cookie, char *buf, size_t size);
typedef ssize_t
(*cookie_write_function_t)(void *cookie, const char *buf, size_t size);
typedef int
(*cookie_seek_function_t)(void *cookie, off64_t *offset, int whence);
typedef int
(*cookie_close_function_t)(void *cookie);
typedef struct {
cookie_read_function_t *read;
cookie_write_function_t *write;
cookie_seek_function_t *seek;
cookie_close_function_t *close;
} cookie_io_functions_t;
FILE *
fopencookie(void *cookie, const char *mode,
cookie_io_functions_t io_funcs);
DESCRIPTION
The fopencookie function associates a stream with up to four "I/O
functions". 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 write
function is omitted, data written to the stream is discarded. If the
close function is omitted, closing the stream will flush any buffered
output and then succeed.
The calling conventions of read, write, and close must match those,
respectively, of read(2), write(2), and close(2) with the single
exception that they are passed the cookie argument specified to
fopencookie in place of the traditional file descriptor argument. The
seek function updates the current stream offset using *offset and whence.
If *offset is non-NULL, it updates *offset with the current stream
offset.
fopencookie is implemented as a thin shim around the funopen(3)
interface. Limitations, possibilities, and requirements of that
interface apply to fopencookie.
RETURN VALUES
Upon successful completion, fopencookie returns a FILE pointer.
Otherwise, NULL is returned and the global variable errno is set to
SEE ALSO
fcntl(2), open(2), fclose(3), fopen(3), fseek(3), funopen(3)
HISTORY
The funopen() functions first appeared in 4.4BSD. The fopencookie
function first appeared in FreeBSD 11.
BUGS
The fopencookie function is a nonstandard glibc extension and may not be
portable to systems other than FreeBSD and Linux.
FreeBSD 14.0-RELEASE-p6 May 9, 2016 FreeBSD 14.0-RELEASE-p6