stdio-common/tmpnam.c

   1 /* Copyright (C) 1991-2024 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 <stdio.h>
  19 #include <string.h>
  20 #include "tmpdir.h"
  21
  22 static char tmpnam_buffer[L_tmpnam];
  23
  24 /* Generate a unique filename in P_tmpdir.
  25
  26    This function is *not* thread safe!  */
  27 char *
  28 tmpnam (char s[L_tmpnam])
  29 {
  30   /* By using two buffers we manage to be thread safe in the case
  31      where S != NULL.  */
  32   char tmpbufmem[L_tmpnam];
  33   char *tmpbuf = s ?: tmpbufmem;
  34
  35   /* In the following call we use the buffer pointed to by S if
  36      non-NULL although we don't know the size.  But we limit the size
  37      to L_tmpnam characters in any case.  */
  38   if (__builtin_expect (__path_search (tmpbuf, L_tmpnam, NULL, NULL, 0),
  39                         0))
  40     return NULL;
  41
  42   if (__glibc_unlikely (__gen_tempname (tmpbuf, 0, 0, __GT_NOCREATE)))
  43     return NULL;
  44
  45   if (s == NULL)
  46     return (char *) memcpy (tmpnam_buffer, tmpbuf, L_tmpnam);
  47
  48   return s;
  49 }
  50
  51 link_warning (tmpnam,
  52               "the use of `tmpnam' is dangerous, better use `mkstemp'")