传值与传引用

传引用相比于传值具有以下优点：
1.能够避免拷贝构造函数和临时对象的析构函数的调用开销；

2.能够避免将派生类对象传递给基类形参时产生的切割现象，切割现象会将派生类所具有的特性都切割掉，变成一个简单的基类对象。

#include<iostream>using namespace std;class Base{public:Base(){}virtual void display(){cout<<"Base::display()"<<endl;}Base(const Base& rhy){cout<<"Base::Base(const Base& rhy)"<<endl;}virtual ~Base(){cout<<"Base::~Base()"<<endl;}};class Derived:public Base{public:Derived():Base(){}void display() override{cout<<"Derived::display()"<<endl;}Derived(const Derived& rhy):Base(rhy){cout<<"Derived::Derived(const Derived& rhy)"<<endl;}~Derived(){cout<<"Derived::~Derived()"<<endl;} };Base function(Base demo){demo.display();return demo;}Base& function2(Base& demo){demo.display();return demo;}int main(){Derived derived;cout<<"传值下的函数调用与切割现象"<<endl; function(derived);cout<<"传引用下的函数调用，无切割现象"<<endl;function2(derived);system("pause");//观察main函数退出之前的函数调用情况 }