sysdeps/posix/mkstemp.c

   1 /* Copyright (C) 1991, 1992, 1996 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 Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    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    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <errno.h>
  22 #include <stdio.h>
  23 #include <fcntl.h>
  24 #include <unistd.h>
  25
  26 /* Generate a unique temporary file name from TEMPLATE.
  27    The last six characters of TEMPLATE must be "XXXXXX";
  28    they are replaced with a string that makes the filename unique.
  29    Returns a file descriptor open on the file for reading and writing.  */
  30 int
  31 mkstemp (template)
  32      char *template;
  33 {
  34   static const char letters[]
  35     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  36   size_t len;
  37   size_t i;
  38
  39   len = strlen (template);
  40   if (len < 6 || strcmp (&template[len - 6], "XXXXXX"))
  41     {
  42       __set_errno (EINVAL);
  43       return -1;
  44     }
  45
  46   if (sprintf (&template[len - 5], "%.5u",
  47                (unsigned int) getpid () % 100000) != 5)
  48     /* Inconceivable lossage.  */
  49     return -1;
  50
  51   for (i = 0; i < sizeof (letters); ++i)
  52     {
  53       int fd;
  54
  55       template[len - 6] = letters[i];
  56
  57       fd = open (template, O_RDWR|O_CREAT|O_EXCL, 0666);
  58       if (fd >= 0)
  59         return fd;
  60     }
  61
  62   /* We return the null string if we can't find a unique file name.  */
  63   template[0] = '\0';
  64   return -1;
  65 }