lib/strcasecmp.c

   1 /* Case-insensitive string comparison function.
   2    Copyright (C) 1998-1999, 2005-2007, 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include <string.h>
  21
  22 #include <ctype.h>
  23 #include <limits.h>
  24
  25 /* Compare strings S1 and S2, ignoring case, returning less than, equal to or
  26    greater than zero if S1 is lexicographically less than, equal to or greater
  27    than S2.
  28    Note: This function does not work with multibyte strings!  */
  29
  30 int
  31 strcasecmp (const char *s1, const char *s2)
  32 {
  33   const unsigned char *p1 = (const unsigned char *) s1;
  34   const unsigned char *p2 = (const unsigned char *) s2;
  35   unsigned char c1, c2;
  36
  37   if (p1 == p2)
  38     return 0;
  39
  40   do
  41     {
  42       c1 = tolower (*p1);
  43       c2 = tolower (*p2);
  44
  45       if (c1 == '\0')
  46         break;
  47
  48       ++p1;
  49       ++p2;
  50     }
  51   while (c1 == c2);
  52
  53   if (UCHAR_MAX <= INT_MAX)
  54     return c1 - c2;
  55   else
  56     /* On machines where 'char' and 'int' are types of the same size, the
  57        difference of two 'unsigned char' values - including the sign bit -
  58        doesn't fit in an 'int'.  */
  59     return _GL_CMP (c1, c2);
  60 }