C String: startsWith, endsWith, indexOf, lastIndexOf in ANSI C

Introduction

This article describe how to implement several function with respect to the index of string, including startsWith, endsWith, indexOf, indexOf with a shift and lastIndexOf.

The Program

startsWith_endsWith_indexOf_lastIndexOf.c

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
/**
 * 
 * Tested with Dev-C++ 4.9.9.2
 *  
 * Practice of string compare.
 *
 * char * strstr ( const char *, const char * ); 
 *            Locate substring
 *            Returns a pointer to the first occurrence of str2 in str1,
 *            or a null pointer if str2 is not part of str1.
 * bool startsWith (char* base, char* str);
 *            Custom function for detecting whether base is starts with str
 * bool endsWith (char* base, char* str);
 *            Custom function for detecting whether base is ends with str
 * int indexOf (char* base, char* str)
 *            Custom function for getting the first index of str in base
 *            -1 denotes not found
 * int indexOf_shift (char* base, char* str, int startIndex)
 *            Custom function for getting the first index of str in base
 *            after the given startIndex
 *            -1 denotes not found
 * int lastIndexOf (char* base, char* str)
 *            Custom function for getting the last index of str in base
 *            -1 denotes not found
 * References: 
 *        http://www.cplusplus.com/reference/cstring/strstr/
 * 
 */

bool startsWith (char* base, char* str);
bool endsWith (char* base, char* str);
int indexOf (char* base, char* str);
int indexOf_shift (char* base, char* str, int startIndex);
int lastIndexOf (char* base, char* str);
int main () {
    // a char array without '\0'
    char* chArrOne = "abcdefabcdef";

    printf("chArrOne starts with abc?\n%s\n\n", startsWith(chArrOne, "abc")? "true" : "false");
    printf("chArrOne starts with def?\n%s\n\n", startsWith(chArrOne, "def")? "true" : "false");
    printf("chArrOne ends with def?\n%s\n\n", endsWith(chArrOne, "def")? "true" : "false");
    printf("first index of abc in chArrOne?\n%d\n\n", indexOf(chArrOne, "abc"));
    printf("first index of def in chArrOne?\n%d\n\n", indexOf(chArrOne, "def"));
    printf("first index of abc in chArrOne after index 2?\n%d\n\n", indexOf_shift(chArrOne, "abc", 2));
    printf("first index of def in chArrOne after index 5?\n%d\n\n", indexOf_shift(chArrOne, "def", 5));
    printf("last index of abc in chArrOne?\n%d\n\n", lastIndexOf(chArrOne, "abc"));
    printf("last index of def in chArrOne?\n%d\n\n", lastIndexOf(chArrOne, "def"));
    

    system("PAUSE");
    return 0;
}
/** detecting whether base is starts with str
 */
bool startsWith (char* base, char* str) {
    return (strstr(base, str) - base) == 0;
}
/** detecting whether base is ends with str
 */
bool endsWith (char* base, char* str) {
    int blen = strlen(base);
    int slen = strlen(str);
    return (blen >= slen) && (0 == strcmp(base + blen - slen, str));
}
/** getting the first index of str in base
 */
int indexOf (char* base, char* str) {
    return indexOf_shift(base, str, 0);
}
int indexOf_shift (char* base, char* str, int startIndex) {
    int result;
    int baselen = strlen(base);
    // str should not longer than base
    if (strlen(str) > baselen || startIndex > baselen) {
        result = -1;
    } else {
        if (startIndex < 0 ) {
            startIndex = 0;
        }
        char* pos = strstr(base+startIndex, str);
        if (pos == NULL) {
            result = -1;
        } else {
            result = pos - base;
        }
    }
    return result;
}
/** use two index to search in two part to prevent the worst case
 * (assume search 'aaa' in 'aaaaaaaa', you cannot skip three char each time)
 */
int lastIndexOf (char* base, char* str) {
    int result;
    // str should not longer than base
    if (strlen(str) > strlen(base)) {
        result = -1;
    } else {
        int start = 0;
        int endinit = strlen(base) - strlen(str);
        int end = endinit;
        int endtmp = endinit;
        while(start != end) {
            start = indexOf_shift(base, str, start);
            end = indexOf_shift(base, str, end);

            // not found from start
            if (start == -1) {
                end = -1; // then break;
            } else if (end == -1) {
                // found from start
                // but not found from end
                // move end to middle
                if (endtmp == (start+1)) {
                    end = start; // then break;
                } else {
                    end = endtmp - (endtmp - start) / 2;
                    if (end <= start) {
                        end = start+1;
                    }
                    endtmp = end;
                }
            } else {
                // found from both start and end
                // move start to end and
                // move end to base - strlen(str)
                start = end;
                end = endinit;
            }
        }
        result = start;
    }
    return result;
}

The Result

Reference

strstr
http://www.cplusplus.com/reference/cstring/strstr/

Download

startsWith_endsWith_indexOf_lastIndexOf.c at github
https://github.com/benbai123/C_Cplusplus_Practice/blob/master/C_StringProcessing/utils/startsWith_endsWith_indexOf_lastIndexOf.c