编写函数，模拟实现strcmp

需要注意两点：

1. 不受限制的字符串函数都是以’\0’为结尾标记来判断的，因此输入参数必须包含‘\0’
2. strcmp不会修改参数值，传参时要加上const修饰

程序代码如下：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

//减法运算判断
int MyStrcmp1(const char *src, const char *dest)
{
	assert(NULL != dest && NULL != src);

	int ret = 0;
	while (!(ret = *(unsigned char *)src - *(unsigned char *)dest) && *dest)
	{
		src++;
		dest++;
	}
	if (ret < 0)
	{
		ret = -1;
	}
	else if (ret > 0)
	{
		ret = 1;
	}
	return ret;
}

//比较运算判断
int MyStrcmp2(const char* dest, const char* src)
{
	assert(NULL != dest && NULL != src);

	while ((*dest) && (*src == *dest))
	{
		*dest++;
		*src++;
	}

	if (*(unsigned char*)dest > *(unsigned char*)src)
		return 1;
	else if (*(unsigned char*)dest < *(unsigned char*)src)
		return -1;
    else
		return 0;
}

int main()
{
	char str1[8] = "hehao";
	char str2[6] = "hello";
	printf("%d\n", MyStrcmp1(str1, str2));
	printf("%d\n", MyStrcmp1("hello", "hello"));
	printf("%d\n", MyStrcmp1("he", "hello"));
	printf("%d\n\n", MyStrcmp1("hello", "he"));

	printf("%d\n", MyStrcmp2(str1, str2));
	printf("%d\n", MyStrcmp2("hello", "hello"));
	printf("%d\n", MyStrcmp2("he", "hello"));
	printf("%d\n", MyStrcmp2("hello", "he"));
	system("pause");
	return 0;
}

           

程序运行结果如下：