How to use the strlen function in C language?

The strlen function is used to calculate the length of a string, and its declaration is as follows:

size_t strlen(const char *str);

其中，str是一个指向字符串的指针，函数返回字符串的长度，不包括字符串末尾的空字符’\0’。

Here is how to use it:

#include <stdio.h>
#include <string.h>

int main() {
    char str[] = "Hello, World!";
    size_t len = strlen(str);
    printf("字符串的长度为：%zu\n", len);
    return 0;
}

The output is: the length of the string is 13.