C++学习笔记(6)----基类和派生类的构造函数和析构函数的执行顺序

基类和派生类：构造函数和析构函数的执行顺序

在Visual Studio中，新建控制台工程，构造类如下：

#include<iostream>
using namespace std;

class CBase {
public:
    CBase() {
        cout << "CBase():Constructor" << endl;
    }
    ~CBase() {
        cout << "CBase(): Destructor" << endl;
    }
};

class CDerive :public CBase {
public:
    CDerive() {
        cout << "CDerive():Constructor" << endl;
    }
    ~CDerive() {
        cout << "CDerive(): Destructor" << endl;
    }
};

对应不同的指针进行 delete 操作，结果如下：

(i)

int main(int argc, char* argv[])
{
    CBase* p = new CDerive();
    delete p;
    return 0;
}

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CBase(): Destructor

(ii)

int main(int argc, char* argv[])
{
    CDerive* pp = new CDerive();
    delete pp;
    return 0;
}

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CDerive(): Destructor
CBase(): Destructor

(iii)

int main(int argc, char* argv[])
{
    CDerive* pp = new CDerive();
    CBase * p = (CBase*)pp;
    delete p;
    return 0;
}

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CBase(): Destructor

(iv)

int main(int argc, char* argv[])
{
    CBase * p = new CDerive();
    CDerive * pp = (CDerive*)p;
    delete pp;
    return 0;
}

运行结果：

S:\ComputerTech\VS2015\Release>Test.exe
CBase():Constructor
CDerive():Constructor
CDerive(): Destructor
CBase(): Destructor

总结：
由上面的实验结果可以看出，当 new CDerive() 时，会先运行基类的构造函数，然后再运行派生类的构造函数；
而当 delete pointer 时，编译器只考虑 pointer 指针本身的类型而不关心 pointer 实际指向的类型，即：若 pointer 为基类指针，则只调用基类的析构函数(不管 pointer 实际指向的是基类还是派生类)；若 pointer 是派生类指针，则先调用派生类的析构函数，再调用基类的析构函数，调用顺序与调用构造函数的顺序相反。