micropolis

Fork

/* 
 * 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;
}