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 of 10 * this file, and for a DISCLAIMER OF ALL WARRANTIES. 11 * 12 * RCS: @(#) $Id: strstr.c,v 1.7 2007/04/16 13:36:34 dkf 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 location of the 29 * first matching instance of substring in string. If string doesn't 30 * contain substring, the return value is 0. Matching is done on an exact 31 * character-for-character basis with no wildcards or special characters. 32 * 33 * Side effects: 34 * None. 35 * 36 *---------------------------------------------------------------------- 37 */ 38 39char * 40strstr( 41 register char *string, /* String to search. */ 42 char *substring) /* Substring to try to find in string. */ 43{ 44 register char *a, *b; 45 46 /* 47 * First scan quickly through the two strings looking for a 48 * single-character match. When it's found, then compare the rest of the 49 * substring. 50 */ 51 52 b = substring; 53 if (*b == 0) { 54 return string; 55 } 56 for ( ; *string != 0; string += 1) { 57 if (*string != *b) { 58 continue; 59 } 60 a = string; 61 while (1) { 62 if (*b == 0) { 63 return string; 64 } 65 if (*a++ != *b++) { 66 break; 67 } 68 } 69 b = substring; 70 } 71 return NULL; 72} 73