c/c++ 常见的标准库函数实现------strlen

int strlen(char *t){

    int length = 0;

    if(t == NULL)

        return -1;

    while (*t != '\0') {

        t++;

        length++;

    }

    return length;

}

size_t strlen(const char *s)

{

    const char *sc;

    for (sc = s; *sc != '\0'; ++sc);

    return sc - s;//因为每次移动的单位是一个字节

}