构造函数调用顺序：Base::Constructor->Sub::Constructor
析构函数调用顺序：Sub::Destructor->Base::Destructor
一个类中只能有一个默认构造函数（提供了无参数构造函数或者默认参数构造函数，都属于默认构造函数，只能选其一）

基本

#include
using namespace std;

class Base {
public:
Base() { cout << “Base:Base()” << endl;}
virtual ~Base() { cout << “Base:~Base()” << endl;}

virtual void showInfo() { cout << "Base::showInfo()" << endl;}

};

class Sub : public Base {
private:
int data;
public:
//Sub() {data = 0;} //默认构造函数（只选其一）
Sub(int data=4) {this->data = data; cout << “Sub:~Sub(int data=4)” << endl;} //默认构造函数（只选其一）
void v3() { cout << “Call Sub::v3, data = “ << data << endl; }

~Sub() {cout << "Sub:~Sub()" << endl;}

virtual void showInfo() { cout << "Sub::showInfo()" << endl;}

};

int main(int argc, char** argv) {

Sub* s = new Sub();
s->showInfo();
delete s;

Base* s2 = new Sub();
s2->showInfo();
delete s2; 
/*如果基类析构函数不加virtual;这样的删除只能属于静态编译调用的是基类析构，
所以只删除基类对象，而我们想要的是调用Sub类析构(Sub类析构会自动调用Base类析构)
*/
return 0;

}

私有构造/析构函数

class singleton {
private:
singleton() {}
~singleton() {}

public:
static singleton* GetSingleton(){
return new singleton();
}
};