[micropolis] / src / tcl / compat / strstr.c

/* 
 * strstr.c --
 *
 *      Source code for the "strstr" library routine.
 *
 * Copyright 1988-1991 Regents of the University of California
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appears in all copies.  The University of California
 * makes no representations about the suitability of this
 * software for any purpose.  It is provided "as is" without
 * express or implied warranty.
 */

#ifndef lint
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)";
#endif /* not lint */

/*
 *----------------------------------------------------------------------
 *
 * strstr --
 *
 *      Locate the first instance of a substring in a string.
 *
 * Results:
 *      If string contains substring, the return value is the
 *      location of the first matching instance of substring
 *      in string.  If string doesn't contain substring, the
 *      return value is 0.  Matching is done on an exact
 *      character-for-character basis with no wildcards or special
 *      characters.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

char *
strstr(string, substring)
    register char *string;      /* String to search. */
    char *substring;            /* Substring to try to find in string. */
{
    register char *a, *b;

    /* First scan quickly through the two strings looking for a
     * single-character match.  When it's found, then compare the
     * rest of the substring.
     */

    b = substring;
    if (*b == 0) {
        return string;
    }
    for ( ; *string != 0; string += 1) {
        if (*string != *b) {
            continue;
        }
        a = string;
        while (1) {
            if (*b == 0) {
                return string;
            }
            if (*a++ != *b++) {
                break;
            }
        }
        b = substring;
    }
    return (char *) 0;
}