stdio-common/tmpnam.c

   1 /* Copyright (C) 1991-2017 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    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <stdio.h>
  19 #include <string.h>
  20
  21 static char tmpnam_buffer[L_tmpnam];
  22
  23 /* Generate a unique filename in P_tmpdir.
  24
  25    This function is *not* thread safe!  */
  26 char *
  27 tmpnam (char *s)
  28 {
  29   /* By using two buffers we manage to be thread safe in the case
  30      where S != NULL.  */
  31   char tmpbufmem[L_tmpnam];
  32   char *tmpbuf = s ?: tmpbufmem;
  33
  34   /* In the following call we use the buffer pointed to by S if
  35      non-NULL although we don't know the size.  But we limit the size
  36      to L_tmpnam characters in any case.  */
  37   if (__builtin_expect (__path_search (tmpbuf, L_tmpnam, NULL, NULL, 0),
  38                         0))
  39     return NULL;
  40
  41   if (__glibc_unlikely (__gen_tempname (tmpbuf, 0, 0, __GT_NOCREATE)))
  42     return NULL;
  43
  44   if (s == NULL)
  45     return (char *) memcpy (tmpnam_buffer, tmpbuf, L_tmpnam);
  46
  47   return s;
  48 }
  49
  50 link_warning (tmpnam,
  51               "the use of `tmpnam' is dangerous, better use `mkstemp'")