typeid测试

#include<iostream>#include<vector>#include<algorithm>using namespace std;class Base {virtual int fun(){}};class Derived: public Base {int fun(){}};int main(){Base* bp1 = new Base();Base* bp2 = new Derived();Derived* dp = new Derived(); cout << (typeid(*bp1) == typeid(Base)) << endl;//1cout << (typeid(*bp1) == typeid(Derived)) << endl;//0 cout << (typeid(*bp2) == typeid(Base)) << endl;//0 cout << (typeid(*bp2) == typeid(Derived)) << endl;//1 cout << (typeid(*dp) == typeid(Base)) << endl;//0 cout << (typeid(*dp) == typeid(Derived)) << endl;//1return 0;} 

如果不定义虚函数，影响的是指向子类型的父类型指针

 

#include<iostream>#include<vector>#include<algorithm>using namespace std;class Base {};class Derived: public Base {};int main(){Base* bp1 = new Base();Base* bp2 = new Derived();Derived* dp = new Derived(); cout << (typeid(*bp1) == typeid(Base)) << endl;//1cout << (typeid(*bp1) == typeid(Derived)) << endl;//0 cout << (typeid(*bp2) == typeid(Base)) << endl;//1 cout << (typeid(*bp2) == typeid(Derived)) << endl;//0 cout << (typeid(*dp) == typeid(Base)) << endl;//0 cout << (typeid(*dp) == typeid(Derived)) << endl;//1return 0;} 

 

原因很简单，只有父类中定义了虚函数，才能实现运行时绑定。此时使用

Base* bp2 = new Derived();

typeid(*dp)得到的是Derived而不是Base