error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'std::string'

    坑爹的VC++，今天用VS2013测试一段代码，结果这个代码竟然提示错误：

string str = "Hello";
cout << str;

error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion)

真是奇葩啊，用CodeBlocks从来不会出这个问题啊，后来 #include<string> 解决，不知道MSVC怎么想的！