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 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 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 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.
[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.
OpenBSD 3.6 June 9, 1993
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