实现strlen、strcpy、strncpy、strcat、strncat

#include <stdio.h> size_t my_strlen(const char *src) { size_t len = 0; while (*src != '\0') { len++; src++; } return len; } char *my_strcpy(char *dest, const char *src) { if (dest == NULL || src == NULL) // 判断输入的字符是否为空 { return NULL; // 如果为空，就返回空 } char *temp = dest; // 将dest的地址赋值给一个临时变量 while (*src != '\0') // 遍历要拷贝的字符 { *temp = *src; // 将src的值赋给temp src++; // src地址后移 temp++; // temp地址后移 } *temp = '\0'; // 最后一位为\0 return dest; // 返回dest } char *my_strncpy(char *dest, const char *src, size_t n) { if (dest == NULL || src == NULL) { return NULL; } char *temp = dest; size_t i; for (i = 0; (i < n) && (*src != '\0'); i++) { *temp = *src; src++; temp++; } for (; i < n; i++) { *temp = '\0'; } return dest; } char *my_strcat(char *dest, const char *src) { if (dest == NULL || src == NULL) { return NULL; } char *temp = dest; while (*temp != '\0') { temp++; } while (*src != '\0') { *temp = *src; temp++; src++; } *temp = '\0'; return dest; } char *my_strncat(char *dest, const char *src, size_t n) { if (dest == NULL || src == NULL) { return NULL; } char *temp = dest; while (*temp != '\0') { temp++; } size_t i; for (i = 0; (i < n) && (*src != '\0'); i++) { *temp = *src; src++; temp++; } for (; i < n; i++) { *temp = '\0'; } return dest; } int main() { char dest[100] = "Hello World"; char src[100] = "Hello World"; // char *result1 = my_strcpy(dest, src); // char *result2 = my_strncpy(dest, src, 3); // size_t result = my_strlen(src); // char *result3 = my_strcat(dest, src); char *result4 = my_strncat(dest, src, 3); // printf("%s\n", result1); // printf("%s\n", result2); // printf("%ld\n", result); // printf("%s\n", result3); printf("%s\n", result4); return 0; }