C#调运C++的DLL返回中文字符串乱码问题

C++ DLL

char * Str_Char(const string &str)
{
	char *data;
	int len = str.length();
	data = (char *)malloc((len+1)*sizeof(char));
	str.copy(data,len,0);
	return data;
}

extern "C" __declspec(dllexport) char* GetStr()
{
	string s1 = "大大";
	return Str_Char(s1);
}char * Str_Char(const string &str)