匹配字符串

char* strstr(const char* str,const char* target)
{
	if(!*target)return NULL;
	char* p1 = (char*)str;
	while(*p1)
	{
		char* p1Begin = p1;
		char* p2 = (char*)target;
		while(*p1 && *p2 && *p1==*p2)
		{
			p1++;
			p2++;
		}
		if(!*p2)return p1Begin;
		p1 = p1Begin+1;
	}
	return NULL;
}