| FUNOPEN(3) | Library Functions Manual | FUNOPEN(3) | 
funopen, funopen2,
  fropen, fropen2,
  fwopen, fwopen2 —
#include <stdio.h>
FILE *
  
  funopen(void *cookie,
    int (*readfn)(void *, char *, int),
    int (*writefn)(void *, const char *, int),
    off_t (*seekfn)(void *, off_t, int),
    int (*closefn)(void *));
FILE *
  
  funopen2(void *cookie,
    ssize_t (*readfn)(void *, void *, size_t),
    ssize_t (*writefn)(void *, const void *, size_t),
    off_t (*seekfn)(void *, off_t, int),
    int (*flushfn)(void *), int
    (*closefn)(void *));
FILE *
  
  fropen(void
    *cookie, int
    (*readfn)(void *, char *, int));
FILE *
  
  fropen2(void
    *cookie, ssize_t
    (*readfn)(void *, void *, size_t));
FILE *
  
  fwopen(void
    *cookie, int
    (*writefn)(void *, const char *, int));
FILE *
  
  fwopen2(void
    *cookie, ssize_t
    (*writefn)(void *, const void *, size_t));
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.
The funopen2() function provides sightly
    different read and write signatures, which match the corresponding system
    calls better, plus the ability to augment the stream's default flushing
    function. If a flushing function is provided, it is called after all data
    has been written to the 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.
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.
funopen() returns a
  FILE pointer. Otherwise, NULL
  is returned and the global variable errno is set to
  indicate the error.
funopen() functions first appeared in
  4.4BSD. The funopen2()
  functions first appeared in NetBSD 7.0.
| March 16, 2012 | NetBSD 9.4 |