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FUNOPEN(3)            DragonFly Library Functions Manual            FUNOPEN(3)


NAME

     funopen, fropen, fwopen - open a stream


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #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(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) with
     the single exception 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), fopencookie(3), fseek(3),
     setbuf(3)


HISTORY

     The funopen() functions first appeared in 4.4BSD.


BUGS

     The funopen() function may not be portable to systems other than BSD.

     The funopen() interface erroneously assumes that fpos_t is an integral
     type; see fseek(3) for a discussion of this issue.

DragonFly 6.5-DEVELOPMENT      February, 4 2023      DragonFly 6.5-DEVELOPMENT

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