stdio-common/perror.c

   1 /* Copyright (C) 1991-2021 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <stdio.h>
  20 #include <string.h>
  21 #include <unistd.h>
  22 #include <wchar.h>
  23 #include "libioP.h"
  24
  25 static void
  26 perror_internal (FILE *fp, const char *s, int errnum)
  27 {
  28   char buf[1024];
  29   const char *colon;
  30   const char *errstring;
  31
  32   if (s == NULL || *s == '\0')
  33     s = colon = "";
  34   else
  35     colon = ": ";
  36
  37   errstring = __strerror_r (errnum, buf, sizeof buf);
  38
  39   (void) __fxprintf (fp, "%s%s%s\n", s, colon, errstring);
  40 }
  41
  42
  43 /* Print a line on stderr consisting of the text in S, a colon, a space,
  44    a message describing the meaning of the contents of `errno' and a newline.
  45    If S is NULL or "", the colon and space are omitted.  */
  46 void
  47 perror (const char *s)
  48 {
  49   int errnum = errno;
  50   FILE *fp;
  51   int fd = -1;
  52
  53
  54   /* The standard says that 'perror' must not change the orientation
  55      of the stream.  What is supposed to happen when the stream isn't
  56      oriented yet?  In this case we'll create a new stream which is
  57      using the same underlying file descriptor.  */
  58   if (__builtin_expect (_IO_fwide (stderr, 0) != 0, 1)
  59       || (fd = __fileno (stderr)) == -1
  60       || (fd = __dup (fd)) == -1
  61       || (fp = fdopen (fd, "w+")) == NULL)
  62     {
  63       if (__glibc_unlikely (fd != -1))
  64         __close (fd);
  65
  66       /* Use standard error as is.  */
  67       perror_internal (stderr, s, errnum);
  68     }
  69   else
  70     {
  71       /* We don't have to do any special hacks regarding the file
  72          position.  Since the stderr stream wasn't used so far we just
  73          write to the descriptor.  */
  74       perror_internal (fp, s, errnum);
  75
  76       if (_IO_ferror_unlocked (fp))
  77         stderr->_flags |= _IO_ERR_SEEN;
  78
  79       /* Close the stream.  */
  80       fclose (fp);
  81     }
  82 }
  83 libc_hidden_def (perror)