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c语言string.h头文件字符串检验函数仿写
所需头文件：stdio.h ,stdlib.h, string.h
strlen字符串求长度
int strlen_my(const char* src_str){ if (NULL == src_str){return -1;}const char* p = src_str;while (*p != '\0'){p++;}return p - &(src_str[0]);}//递归int strlen_my2(const char* src_str){if (src_str == NULL)return -1;if (*src_str){return strlen_my2(src_str + 1) + 1;}else{return 0;}} int main(){const char* p = "hello";printf("%d \n",strlen_my(p));return 0;}strcmp / strncmp字符串比较
int strcmp_my(const char* str_a, const char* str_b){while ((*str_a != '\0' || *str_b != '\0') && *str_a == *str_b ){str_a++;str_b++;} return *str_a - *str_b > 0 ? 1 : (*str_a - * str_b < 0 ? -1 : 0);}int strcmp_my2(const char* str_a, const char* str_b){int sub = 0;while ((sub = *str_a - *str_b) == 0 && *str_a++ && *str_b++);//先赋值，指针再++ return sub > 0 ? 1 : (sub < 0 ? -1 : 0);} int strncmp_my(const char* str_a, const char* str_b, size_t front_len){while (--front_len && *str_a != '\0' && *str_b != '\0' && *str_a == *str_b){str_a++;str_b++;} return *str_a - *str_b > 0 ? 1 : (*str_a - *str_b < 0 ? -1 : 0);} int main(){const char* p = "hella";const char* q = "hell";printf("%d \n", strncmp_my(p, q, 4));return 0;}strchr / strrchr 字符串中查找字符ch
第一个出现的字符ch
//strchr 返回字符串中第一个出现的字符chchar* strchr_my(const char* src_str, char ch){if (src_str == NULL){return NULL;} while (*src_str != '\0' && *src_str != ch){src_str++;} return *src_str == '\0' ? NULL : src_str;} int main(){const char* p = "hello";p = strchr_my(p, 'e');if (p == NULL)return 0;printf("%c\n", *p);}最后一个出现的字符ch
//strrchr查找字符串中最后一个出现的字母chchar* strrchr_my(const char* src_str, char ch){if (NULL == src_str) return NULL;const char* p = src_str + strlen(src_str) - 1; while ((p - src_str) >= 0 && *p != ch){p--;}if (p - src_str == -1){return NULL;}return p;} int main(){const char* p = "hello";//p = strchr_my(p, 'q'); p = strrchr_my(p, 'l');if (p == NULL)return 0;printf("%c\n", *p);}strstr 字符串匹配：src_str中查找des_str，返回匹配的起始位置，没有为NULL（BF算法）
char* strstr_my(const char* src_str, const char* des_str){if (NULL == src_str || NULL == des_str){return NULL;} int len_src = strlen(src_str);int len_des = strlen(des_str);int i = 0;//src_strint j = 0;//des_str while (i < len_src && j < len_des){if (src_str[i] == des_str[j]){i++;j++;}else{i = i - j + 1;j = 0;}} if (j == len_des){return src_str + i - j;}return NULL;} int main(){const char* p = "hello";const char* q = "llo";const char* rt = strstr_my(p, q);if (rt != NULL){printf("%s\n", rt);return 0;}return 0;}strcpy / strncpy字符串拷贝
char* strcpy_my(char* des_str, const char* src_str){if (des_str == NULL || src_str == NULL)return NULL;char* p = des_str;while (*src_str != '\0'){*p++ = *src_str++;}*p = '\0';return des_str;} char* strncpy_my(char* des_str, const char* src_str, size_t len){if (des_str == NULL || src_str == NULL || len <= 0)return NULL;char* p = des_str;//源字符串实际长度int cur_len = strlen(src_str) <= len ? len : strlen(src_str); while (cur_len--){*p++ = *src_str++;}*p = '\0';return des_str;} int main(){const char* p = "hello";char q[10] = {0}; if (strncpy_my(q, p, 1) != NULL){printf("%s\n", q);} return 0;}strcat / strncat字符串的粘贴
char* strcat_my(char* des_str, const char* src_str){if (des_str == NULL || src_str == NULL)return NULL;int len_des = strlen(des_str);char* p = des_str + len_des; while (*src_str != '\0'){*p++ = *src_str++;}return des_str;} char* strncat_my(char* des_str, const char* src_str, size_t len){if (des_str == NULL || src_str == NULL || len < 0)return NULL;int len_des = strlen(des_str);char* p = des_str + len_des; while (len--){*p++ = *src_str++;}return des_str;} int main(){char p[20] = "hello";const char* q = "world";printf("p = %s\n", p);printf("q = %s\n", q);if (strncat_my(p, q, 3) != NULL) {printf("p = %s\n", p);}printf("q = %s\n", q);return 0;}strdup 字符串申请堆区空间存放字符串的副本
char* strdup_my(const char* src_str){if (NULL == src_str)return NULL;char* newspace = (char*)malloc((strlen(src_str) + 1 ) * sizeof(char));if (newspace == NULL)return NULL;int i = 0;while (*src_str != '\0'){newspace[i++] = *src_str++;}newspace[i] = '\0';return newspace;}int main(){const char* p = "hello";char* q = strdup_my(p);if (q != NULL){printf("%s\n", q);free(q);q == NULL;}return 0;}感谢各位的阅读，以上就是“怎么仿写C语言string.h头文件检验字符串函数”的内容了，经过本文的学习后，相信大家对怎么仿写C语言string.h头文件检验字符串函数这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是编程网，小编将为大家推送更多相关知识点的文章，欢迎关注！
