C++ using的多种用法

1、引入命名空间

using namespace std;
using std::cout;

2、引入基类成员

class Base{
public:void func(){cout << "Base::func()" << endl;}
};
class Derived : public Base{
public:using Base::func;void func(int x){cout << "Derived::func(x)" << x << endl;}
};
int main(){Derived d;d.func();	//Base::func()d.func(1);	//Derived::func(x)return 0;
}

3、取别名

//给类型取别名
using type = int;
type x = 10;//给FormatItem类型的智能指针取名为ptr
using ptr = shared_ptr<FormatItem>;template<class T>
class A{
public://给模板类型取别名using value_type = T;//T func(){}value_type func(){}
private://T x;value_type x;
}