C++学习记录（三）析构函数，初始化

这是第三天的学习记录

#include <iostream>

using namespace std;
class B
{
public:
    B() { cout << "B construction !" << endl; }
    ~B() { cout << "B deconstruction !" << endl; }
};

class A
{
    B* b;
public:
    A()
    {
        cout << "A construction !" << endl;
        b = new B;
    }
    // 析构函数的定义格式，用于释放类中指针指向堆区中的空间,对象销毁时自动调用
    ~A()
    {
        cout << "A deconstruction !" << endl;
        delete b;
    }
};


int main()
{
    // 析构函数专门用于清理类中有指针的成员(该成员指向堆区的情况)
    //A a;
    A* pa = new A;
    delete pa;
    cout << "Hello World!" << endl;
    return 0;
}

#include <iostream>

using namespace std;

class B
{
    B()
    {
        cout << "B is construction !" << endl;
    }
    ~B()
    {
        cout << "B is deconstruction !" << endl;
    }
};
class A
{
private:
    const int a;        // 只读变量要在构造时初始化
    static int b;       // 静态成员变量，必需在类外初始化，且只能初始化一次
public:
    // 初始化列表是构造函数的特殊语法，调用时机先于构造函数
    A():a(100)
    {
        cout << "A is construction !" << endl;
    }
    ~A()
    {
        cout << "A is deconstruction !" << endl;
    }
    int getAInfo()
    {
        return a;
    }
    int getBInfo()
    {
        return b;
    }

};

// 静态变量初始化格式:类外，main函数前
int A::b = 200;

int main()
{
    A a;
    cout << a.getAInfo() << endl;
    cout << a.getBInfo() << endl;

    cout << "Hello World!" << endl;
    return 0;
}