source: downloads/tcl8.5.2/compat/strstr.c @ 25

/* 
 * strstr.c --
 *
 *      Source code for the "strstr" library routine.
 *
 * Copyright (c) 1988-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: strstr.c,v 1.7 2007/04/16 13:36:34 dkf Exp $
 */

#include "tcl.h"
#ifndef NULL
#define NULL 0
#endif

/*
 *----------------------------------------------------------------------
 *
 * 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(
    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 NULL;
}