sysdeps/posix/mkstemp.c

   1 /* Copyright (C) 1991, 1992 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
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.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 DEFUN(mkstemp, (template), char *template)
  32 {
  33   static CONST char letters[]
  34     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  35   size_t len;
  36   size_t i;
  37
  38   len = strlen (template);
  39   if (len < 6 || strcmp (&template[len - 6], "XXXXXX"))
  40     {
  41       errno = EINVAL;
  42       return -1;
  43     }
  44
  45   if (sprintf (&template[len - 5], "%.5u",
  46                (unsigned int) getpid () % 100000) != 5)
  47     /* Inconceivable lossage.  */
  48     return -1;
  49
  50   for (i = 0; i < sizeof (letters); ++i)
  51     {
  52       int fd;
  53
  54       template[len - 6] = letters[i];
  55
  56       fd = open (template, O_RDWR|O_CREAT|O_EXCL, 0666);
  57       if (fd >= 0)
  58         return fd;
  59     }
  60
  61   /* We return the null string if we can't find a unique file name.  */
  62   template[0] = '\0';
  63   return -1;
  64 }