c语言字符串匹配算法怎么写

C语言字符串匹配算法有很多种，下面介绍几种常用的算法实现。

Brute-Force算法（朴素算法）

int strStr(char* haystack, char* needle) {    int i, j;    int len1 = strlen(haystack);    int len2 = strlen(needle);        for (i = 0; i <= len1 - len2; i++) {        for (j = 0; j < len2; j++) {            if (haystack[i + j] != needle[j]) {                break;            }        }        if (j == len2) {            return i;        }    }        return -1;}

KMP算法（Knuth-Morris-Pratt算法）

void getNext(char* needle, int* next) {    int i, j;    int len = strlen(needle);        next[0] = -1;    i = 0;    j = -1;    while (i < len) {        if (j == -1 || needle[i] == needle[j]) {            i++;            j++;            next[i] = j;        } else {            j = next[j];        }    }}int strStr(char* haystack, char* needle) {    int i, j;    int len1 = strlen(haystack);    int len2 = strlen(needle);    int* next = (int*)malloc(sizeof(int) * len2);        getNext(needle, next);        i = 0;    j = 0;    while (i < len1 && j < len2) {        if (j == -1 || haystack[i] == needle[j]) {            i++;            j++;        } else {            j = next[j];        }    }        free(next);    if (j == len2) {        return i - j;    } else {        return -1;    }}

Boyer-Moore算法

#define MAX_CHAR 256int max(int a, int b) {    return a > b ? a : b;}void badCharHeuristic(char* needle, int* badChar) {    int i;    int len = strlen(needle);    for (i = 0; i < MAX_CHAR; i++) {        badChar[i] = -1;    }    for (i = 0; i < len; i++) {        badChar[(int)needle[i]] = i;    }}void goodSuffixHeuristic(char* needle, int* goodSuffix) {    int i, j;    int len = strlen(needle);    int* suffix = (int*)malloc(sizeof(int) * (len + 1));        for (i = 0; i <= len; i++) {        suffix[i] = -1;    }        for (i = len - 1; i >= 0; i--) {        if (suffix[i] == -1) {            suffix[i] = len - i - 1;            for (j = 0; j < i; j++) {                if (needle[j] == needle[len - i + j]) {                    suffix[j] = len - i + j;                }            }        }    }        for (i = 0; i < len; i++) {        goodSuffix[i] = len - suffix[i + 1];    }    for (i = 0; i <= len; i++) {        goodSuffix[len] = len - suffix[i + 1];    }        free(suffix);}int strStr(char* haystack, char* needle) {    int i = 0, j = 0;    int len1 = strlen(haystack);    int len2 = strlen(needle);    int badChar[MAX_CHAR];    int* goodSuffix = (int*)malloc(sizeof(int) * (len2 + 1));        badCharHeuristic(needle, badChar);    goodSuffixHeuristic(needle, goodSuffix);        while (i <= len1 - len2) {        j = len2 - 1;        while (j >= 0 && needle[j] == haystack[i + j]) {            j--;        }        if (j < 0) {            free(goodSuffix);            return i;        } else {            i += max(goodSuffix[j], j - badChar[(int)haystack[i + j]]);        }    }        free(goodSuffix);    return -1;}

以上是几种常用的字符串匹配算法的C语言