FILE
*
funopen(
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)
)
)
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);
except that they are passed the
cookie
argument specified to
funopen()
in place of the traditional file descriptor argument,
and
seekfn
uses
fpos_t
instead of
off_t
.
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.
)
returns a
FILE
pointer.
Otherwise,
NULL
is returned and the global variable
errno
is set to indicate the error.
EINVAL
]
)
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).
)
functions first appeared in
4.4BSD.
)
function
may not be portable to systems other than
BSD.