1/*
2 * strstr.c --
3 *
4 *	Source code for the "strstr" library routine.
5 *
6 * Copyright (c) 1988-1993 The Regents of the University of California.
7 * Copyright (c) 1994 Sun Microsystems, Inc.
8 *
9 * See the file "license.terms" for information on usage and redistribution
10 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
11 *
12 * RCS: @(#) $Id: strstr.c,v 1.3.2.1 2005/04/12 18:28:56 kennykb Exp $
13 */
14
15#include <tcl.h>
16#ifndef NULL
17#define NULL 0
18#endif
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
41char *
42strstr(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 NULL;
73}
74