strstr函数及其代码模拟实现

一.用法

定义：char * strstr( const char *str1, const char *str2 );

•判断str1中是否包含子串str2

•若包含，则返回在str1中子串str2首字符的地址

•若不包含，则返回空指针NULL

例：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
int main()
{
	char arr1[] = "zhangsan";
	char arr2[] = "san";
	char* ret = strstr(arr1, arr2);
	if (ret == NULL)
	{
		printf("子串不存在\n");
	}
	else
	{
		printf("子串存在 且为：%s\n", ret);
	}
	return 0;
}

运行结果：

二、代码模拟实现

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
#include<assert.h>

//代码模拟实现
char* my_strstr(const char* str1, const char* str2)
{
	assert(str1 && str2);
	const char* s1 = str1;
	const char* s2 = str2;
	const char* p = str1;

	while (*p)
	{
		s1 = p;
		s2 = str2;
		while (*s1 != '\0' && *s2 != '\0' && *s1 == *s2)
		{
			s1++;
			s2++;
		}
		if (*s2 == '\0')
		{
			return (char*)p;
		}
		p++;
	}
	return NULL;
}

int main()
{
	//char email[] = "[email protected]";
	//char substr[] = "bitejiuyeke";
	//char* ret = my_strstr(email, substr);
	char arr1[] = "zhangsan";
	char arr2[] = "san";
	char* ret = my_strstr(arr1, arr2);

	if (ret == NULL)
	{
		printf("子串不存在\n");
	}
	else
	{
		printf("子串存在，且为：%s\n", ret);
	}
	return 0;
}

运行结果：

以上就是strstr函数的基本用法，欢迎指正~