fileno (3)

PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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, or the stream is not associated with a file.

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

Section 2.5.1, Interaction of File Descriptors and Standard I/O Streams, dirfd(), fdopen(), fopen(), stdin The Base Definitions volume of POSIX.1-2008, <stdio.h>

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see www.kernel.org/doc/man-pages/reporting_bugs.html .