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FUNOPEN(3)                 Library Functions Manual                 FUNOPEN(3)

NAME
     funopen, fropen, fwopen -- open a stream

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <&lt;stdio.h>&gt;

     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 *
     fropen(void  *cookie, int  (*readfn)(void *, char *, int));

     FILE *
     fwopen(void  *cookie, int  (*writefn)(void *, const char *, int));

DESCRIPTION
     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); 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.

RETURN VALUES
     Upon successful completion, funopen() returns a FILE pointer.  Otherwise,
     NULL is returned and the global variable errno is set to indicate the
     error.

ERRORS
     [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).

SEE ALSO
     fcntl(2), open(2), fclose(3), fopen(3), fseek(3), setbuf(3)

HISTORY
     The funopen() functions first appeared in 4.4BSD.

CAVEATS
     All three functions are specific to NetBSD and thus unportable.

NetBSD 6.1.5                   January 22, 2012                   NetBSD 6.1.5