MirOS Manual: fropen(3), funopen(3), fwopen(3)

FUNOPEN(3)                 BSD Programmer's Manual                  FUNOPEN(3)


     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 may be
     given as NULL pointers. 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 as-
     sociated operation on the resulting stream will fail. If the close func-
     tion 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 re-
     cently 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


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


     [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


     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.

MirOS BSD #10-current            June 9, 1993                                1

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