compiler/stdc/strstr.c

   1 /*
   2     Copyright © 1995-2012, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     C99 function strstr().
   6 */
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11 #include <string.h>
  12
  13         char * strstr (
  14
  15 /*  SYNOPSIS */
  16         const char * str,
  17         const char * search)
  18
  19 /*  FUNCTION
  20         Searches for a string in a string.
  21
  22     INPUTS
  23         str - Search this string
  24         search - Look for this string
  25
  26     RESULT
  27         A pointer to the first occurence of search in str or NULL if search
  28         is not found in str.
  29
  30     NOTES
  31
  32     EXAMPLE
  33         char buffer[64];
  34
  35         strcpy (buffer, "Hello ");
  36
  37         // This returns a pointer to the first l in buffer.
  38         strstr (buffer, "llo ");
  39
  40         // This returns NULL
  41         strstr (buffer, "llox");
  42
  43     BUGS
  44
  45     SEE ALSO
  46         strchr(), strrchr(), strpbrk()
  47
  48     INTERNALS
  49
  50 ******************************************************************************/
  51 {
  52     size_t       done;
  53     size_t       len_s = strlen (search);
  54     const char * t;
  55
  56     do
  57     {
  58         /* If the first character matches */
  59         if (*search == *str)
  60         {
  61             /* How many characters to compare */
  62             done = len_s;
  63
  64             /* Skip the first char (we have checked this one already) */
  65             t = search + 1;
  66             str ++;
  67
  68             /*
  69                 Until all characters have been compared and the two
  70                 characters at the current position are equal ...
  71             */
  72             while ((--done) && (*t == *str))
  73             {
  74                 /* Next character */
  75                 t ++;
  76                 str ++;
  77             }
  78
  79             /* All character compared ? */
  80             if (!done)
  81             {
  82                 /*
  83                     Then we have found what we were looking for. str points
  84                     now to the last character of the string we look for.
  85                     Therefore we must move it backward to the beginning of
  86                     the string.
  87                 */
  88                 str -= len_s;
  89                 return ((char *)str);
  90             }
  91             else
  92             {
  93                 /*
  94                     The strings are the same upto this character. I must
  95                     go back since the pattern might be something like
  96                     "ccbba" and the string "cccbba".
  97                 */
  98                 str -= len_s - done;
  99             }
 100         }
 101     } while (*str++);
 102
 103     /* nothing found */
 104     return(0);
 105 } /* strstr */
 106
 107 #ifdef TEST
 108 #include <stdio.h>
 109 #include <string.h>
 110
 111 int main (int argc, char ** argv)
 112 {
 113     char * ptr;
 114
 115     if (argc != 3)
 116     {
 117         printf ("Usage: %s string search\n", argv[0]);
 118         return 10;
 119     }
 120
 121     ptr = strstr (argv[1], argv[2]);
 122
 123     if (!ptr)
 124         printf ("%s not found in %s\n", argv[2], argv[1]);
 125     else
 126         printf ("%s found in %s as %s\n", argv[2], argv[1], ptr);
 127
 128     return 0;
 129 }
 130 #endif /* TEST */