C++ std::string和C字符串之间的问题

#include <string>
#include <iostream>
#include <stdlib.h>

int main(){

//std::string str;
std::string str("");

if (str.c_str() == "")
std::cout << "haha" << std::endl;
else
std::cout << "wuwu" << std::endl;

system("pause");
return 0;
}