git.zerfleddert.de Git - micropolis/blob - src/tcl/compat/strstr.c

   1 /*
   2  * strstr.c --
   3  *
   4  *      Source code for the "strstr" library routine.
   5  *
   6  * Copyright 1988-1991 Regents of the University of California
   7  * Permission to use, copy, modify, and distribute this
   8  * software and its documentation for any purpose and without
   9  * fee is hereby granted, provided that the above copyright
  10  * notice appears in all copies.  The University of California
  11  * makes no representations about the suitability of this
  12  * software for any purpose.  It is provided "as is" without
  13  * express or implied warranty.
  14  */
  15
  16 #ifndef lint
  17 static char rcsid[] = "$Header: /sprite/src/lib/tcl/compat/RCS/strstr.c,v 1.1 91/09/19 16:22:12 ouster Exp $ SPRITE (Berkeley)";
  18 #endif /* not lint */
  19
  20 /*
  21  *----------------------------------------------------------------------
  22  *
  23  * strstr --
  24  *
  25  *      Locate the first instance of a substring in a string.
  26  *
  27  * Results:
  28  *      If string contains substring, the return value is the
  29  *      location of the first matching instance of substring
  30  *      in string.  If string doesn't contain substring, the
  31  *      return value is 0.  Matching is done on an exact
  32  *      character-for-character basis with no wildcards or special
  33  *      characters.
  34  *
  35  * Side effects:
  36  *      None.
  37  *
  38  *----------------------------------------------------------------------
  39  */
  40
  41 char *
  42 strstr(string, substring)
  43     register char *string;      /* String to search. */
  44     char *substring;            /* Substring to try to find in string. */
  45 {
  46     register char *a, *b;
  47
  48     /* First scan quickly through the two strings looking for a
  49      * single-character match.  When it's found, then compare the
  50      * rest of the substring.
  51      */
  52
  53     b = substring;
  54     if (*b == 0) {
  55         return string;
  56     }
  57     for ( ; *string != 0; string += 1) {
  58         if (*string != *b) {
  59             continue;
  60         }
  61         a = string;
  62         while (1) {
  63             if (*b == 0) {
  64                 return string;
  65             }
  66             if (*a++ != *b++) {
  67                 break;
  68             }
  69         }
  70         b = substring;
  71     }
  72     return (char *) 0;
  73 }