FUNOPEN(3) BSD Programmer's Manual FUNOPEN(3)
funopen, fropen, fwopen - open a stream
#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(const void *cookie, int (*readfn)(void *, char *, int));
FILE *
fwopen(const 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 may be
given as NULL pointers. 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 as-
sociated operation on the resulting stream will fail. If the close func-
tion 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 exceptions that they are passed the cookie argument specified to
funopen() in place of the traditional file descriptor argument and that
the seek function takes an fpos_t argument and not an off_t 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 re-
cently 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 er-
ror.
[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).
fcntl(2), open(2), fclose(3), fopen(3), fseek(3), setbuf(3)
The funopen() functions first appeared in 4.4BSD.
The funopen() function may not be portable to systems other than BSD.
MirBSD #10-current June 9, 1993 1