在C语言中，字符串函数可以通过以下两种方式定义：
使用字符数组作为参数和返回值#include <stdio.h>// 字符串长度int my_strlen(char str[]) { int len = 0; while (str[len] != '\0') { len++; } return len;}// 字符串复制void my_strcpy(char dest[], char src[]) { int i = 0; while (src[i] != '\0') { dest[i] = src[i]; i++; } dest[i] = '\0';}// 字符串连接void my_strcat(char dest[], char src[]) { int dest_len = my_strlen(dest); int i, j = 0; for (i = dest_len; src[j] != '\0'; i++, j++) { dest[i] = src[j]; } dest[i] = '\0';}int main() { char str1[100] = "Hello"; char str2[100] = "World"; printf("str1 length: %d\n", my_strlen(str1)); my_strcpy(str1, str2); printf("str1 after copy: %s\n", str1); my_strcat(str1, str2); printf("str1 after concatenation: %s\n", str1); return 0;}#include <stdio.h>// 字符串长度int my_strlen(char *str) { int len = 0; while (*str != '\0') { len++; str++; } return len;}// 字符串复制char* my_strcpy(char *dest, char *src) { char *p = dest; while (*src != '\0') { *dest = *src; dest++; src++; } *dest = '\0'; return p;}// 字符串连接char* my_strcat(char *dest, char *src) { char *p = dest; while(*dest != '\0') { dest++; } while (*src != '\0') { *dest = *src; dest++; src++; } *dest = '\0'; return p;}int main() { char str1[100] = "Hello"; char str2[100] = "World"; printf("str1 length: %d\n", my_strlen(str1)); my_strcpy(str1, str2); printf("str1 after copy: %s\n", str1); my_strcat(str1, str2); printf("str1 after concatenation: %s\n", str1); return 0;}无论使用字符数组还是指针，都可以实现相同的功能。但是需要注意指针的使用需要更谨慎，避免指针操作超出字符串的范围。
