KMP字符串匹配算法 C语言实现

数据结构书上的SString是默认下标0存字符串长度的，改了以下：
如果有错，欢迎指正：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int get_nextval(char *pattern, int next[])
{
    //get the next value of the pattern
    int i = 0, j = -1;
    next[0] = -1;
    int patlen = strlen(pattern);
    while ( i < patlen - 1){
        if ( j == -1 || pattern[i] == pattern[j]){
            ++i;
            ++j;
            if (pattern[i] != pattern[j])
                next[i] = j;
            else
                next[i] = next[j];
        }
        else
            j = next[j];
        }

    return(0);
}

int kmpindex(char *target, char *pattern, int pos)
{
    int tari = pos, pati = 0;
    int tarlen = strlen(target), patlen = strlen(pattern);
    int *next = (int *)malloc(patlen * sizeof(int));
    get_nextval(pattern, next);
    while ( tari < tarlen && pati < patlen ){
        if (pati == -1 ||target[tari] == pattern[pati]){
            ++tari;
            ++pati;
            }else{
                pati = next[pati];
            }
    }
if(next != NULL) free(next);
next = NULL;
if (pati == patlen)
    return tari - pati;
else
    return -1;
}


int main()
{
    char target[50], pattern[50];
    printf("imput the target:\n" );
    scanf("%s",target);
    printf("imput the pattern:\n" );
    scanf("%s",pattern);
    int ans = kmpindex(target,pattern,0);
    if (ans == -1)
        printf("error\n");
    else
        printf("index:%d\n",ans);
    return 0;
}