C语言实现strstr

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

str1为以''结束的被查找的字符串

str2为以''结束的要查找的字符串

被查找字符串："abcdefabcdef"

要查找字符串："def"

strstr返回值为字符串地址：从被查找的字符串中 第一次出现 要查找的字符串的位置 向后打印

#include
#include
#include
#include


const char* my_strstr(const char* p1, const char* p2)
{
	assert(p1 != NULL);
	assert(p2 != NULL);
	char* s1 = (char*)p1;
	char* s2 = (char*)p2;
	char* cur = (char*)p1;
	if (*p2 == '')
	{
		return p1;
	}
	while (*cur)
	{
		s1 = cur;
		s2 = (char*)p2;
		while ((*s1 != '') && (*s2 != '') && (*s1 == *s2))
		{
			s1++;
			s2++;
		}
		if (*s2 == '')
		{
			return cur;
		}
		cur++;
	}
	return NULL;
}

int main()
{
	const char* p1 = "aaabcd";
	const char* p2 = "abc";
	const char* ret = my_strstr(p1, p2);
	if (ret == NULL)
		printf("子串不存在n");
	else
		printf("%s", ret);
	return 0;
}