newlib/libc/stdio/fileno.c

   1 /*
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are permitted
   6  * provided that the above copyright notice and this paragraph are
   7  * duplicated in all such forms and that any documentation,
   8  * and/or other materials related to such
   9  * distribution and use acknowledge that the software was developed
  10  * by the University of California, Berkeley.  The name of the
  11  * University may not be used to endorse or promote products derived
  12  * from this software without specific prior written permission.
  13  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  15  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  16  */
  17
  18 /*
  19 FUNCTION
  20 <<fileno>>, <<fileno_unlocked>>---return file descriptor associated with stream
  21
  22 INDEX
  23         fileno
  24 INDEX
  25         fileno_unlocked
  26
  27 SYNOPSIS
  28         #include <stdio.h>
  29         int fileno(FILE *<[fp]>);
  30
  31         #define _BSD_SOURCE
  32         #include <stdio.h>
  33         int fileno_unlocked(FILE *<[fp]>);
  34
  35 DESCRIPTION
  36 You can use <<fileno>> to return the file descriptor identified by <[fp]>.
  37
  38 <<fileno_unlocked>> is a non-thread-safe version of <<fileno>>.
  39 <<fileno_unlocked>> may only safely be used within a scope
  40 protected by flockfile() (or ftrylockfile()) and funlockfile().  This
  41 function may safely be used in a multi-threaded program if and only
  42 if they are called while the invoking thread owns the (FILE *)
  43 object, as is the case after a successful call to the flockfile() or
  44 ftrylockfile() functions.  If threads are disabled, then
  45 <<fileno_unlocked>> is equivalent to <<fileno>>.
  46
  47 RETURNS
  48 <<fileno>> returns a non-negative integer when successful.
  49 If <[fp]> is not an open stream, <<fileno>> returns -1.
  50
  51 PORTABILITY
  52 <<fileno>> is not part of ANSI C.
  53 POSIX requires <<fileno>>.
  54
  55 <<fileno_unlocked>> is a BSD extension also provided by GNU libc.
  56
  57 Supporting OS subroutines required: none.
  58 */
  59
  60 #include <_ansi.h>
  61 #include <stdio.h>
  62 #include <errno.h>
  63 #include "local.h"
  64
  65 int
  66 fileno (FILE * f)
  67 {
  68   int result;
  69   CHECK_INIT (_REENT, f);
  70   _newlib_flockfile_start (f);
  71   if (f->_flags)
  72     result = __sfileno (f);
  73   else
  74     {
  75       result = -1;
  76       _REENT_ERRNO(_REENT) = EBADF;
  77     }
  78   _newlib_flockfile_end (f);
  79   return result;
  80 }