NAME

       fileno - map a stream pointer to a file descriptor

SYNOPSIS

       #include <stdio.h>

       int fileno(FILE *stream);

DESCRIPTION

       The  fileno()  function shall return the integer file descriptor associated with the stream pointed to by
       stream.

RETURN VALUE

       Upon successful completion, fileno() shall return the integer value of  the  file  descriptor  associated
       with stream.  Otherwise, the value -1 shall be returned and errno set to indicate the error.

ERRORS

       The fileno() function may fail if:

       EBADF  The stream argument is not a valid stream.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       Without  some specification of which file descriptors are associated with these streams, it is impossible
       for an application to set up the streams for another application it  starts  with  fork()  and  exec.  In
       particular,  it would not be possible to write a portable version of the sh command interpreter (although
       there may be other constraints that would prevent that portability).

FUTURE DIRECTIONS

       None.

SEE ALSO

       Interaction of File Descriptors and Standard I/O Streams , fdopen()  ,  fopen()  ,  stdin()  ,  the  Base
       Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                             FILENO(P)