strlen函數(shù)是用來(lái)計(jì)算字符串長(zhǎng)度的一個(gè)函數(shù)，返回類型是size_t

#include<stdio.h>
#include<string.h>
int main()
{
	char arr[] = "hello world";
	size_t;//返回值是size_t unsigned int
	int len = strlen(arr);
	printf("len=%d\n", len);
	return 0;
}

int main()
{
	const char* p1 = "abc";
	const char* p2 = "adbcdef";
	if (strlen(p1) - strlen(p2) > 0)
		//因?yàn)榉祷刂凳菬o(wú)符號(hào)數(shù)，所以沒(méi)有負(fù)數(shù)
	{
		printf("hehe");
	}
	else
	{
		printf("haha");
	}
	return 0;
}

#include<stdio.h>
#include<assert.h>
//模擬實(shí)現(xiàn)strlen
size_t my_strlen(const char* str)
{
	int count = 0;//計(jì)數(shù)器
	assert(str != NULL);
	//斷言不是空指針，如果沒(méi)有這步，當(dāng)是空指針的時(shí)候可能會(huì)崩潰
	while (*str != '\0')
	{
		count++;
		str++;
	}
	return count;
}
int main()
{
	char arr[] = "hello";
	int len = my_strlen(arr);
	printf("%d\n", len);
	return 0;
}

#include<stdio.h>
#include<assert.h>
//不使用臨時(shí)變量
size_t my_strlen(const char* str)
{
	assert(str != NULL);
	if (*str != '\0')
	{
		return 1 + my_strlen(str + 1);
	}
	else
	{
		return 0;
	}
}
int main()
{
	char arr[] = "hello";
	int len = my_strlen(arr);
	printf("%d\n", len);
	return 0;
}

//指針相減的做法
size_t my_strlen(const char* str)
{
	assert(str != NULL);
	const char* start = str;
	//str 不能初始化char類型，所以用const
	while (*str != '\0')
	{
		str++;
	}
	return str - start;
}
int main()
{
	char arr[] = "hello";
	int len = my_strlen(arr);
	printf("%d\n", len);
	return 0;
}