C++类变量构造和析构顺序

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文章目录

继承关系上构造析构顺序
同一级别的构造顺序
析构的顺序则刚好是构造顺序的逆序

继承关系上构造析构顺序

有类静态成员变量优先构造静态变量
- 与声明的顺序无关，与继承关系也无关，只是按照定义的先后顺序构造。
先调用基类的构造
- 先构造基类成员变量
- 基类本身的构造函数
然后再是派生类
- 先构造派生类成员变量
- 派生类本身的构造函数

同一级别的构造顺序

类静态成员与声明的顺序无关，与继承关系也无关，根据定义的先后顺序初始化
类普通成员变量按照定义的顺序初始化
继承关系则是根据继承的先后顺序初始化
有虚函数的先初始化虚表指针
执行初始化列表
执行构造函数

示例：

#include <iostream>using namespace std;class Base
{
public:virtual int size() {cout << "Base::size" << endl;return 22; }
};class A :public Base
{
public:int m_a = -1;A() :m_a(size())   //在初始化列表中调用了虚函数{cout << "in A() m_a is " <<  m_a << endl;}virtual int size() {cout << "A::size" << endl;return 11;}
};int main()
{A a;return 0;
}

output:

A::size
in A() m_a is 11

析构的顺序则刚好是构造顺序的逆序

示例：

#include<iostream>using namespace std;class C
{
public:C() { cout << "in C()" << endl; }~C() { cout << "in ~C()" << endl; }
};class D
{
public:D() { cout << "in D()" << endl; }~D() { cout << "in ~D()" << endl; }
};class StaticA
{
public:StaticA() { cout << "in StaticA()" << endl; }~StaticA() { cout << "in ~StaticA()" << endl; }
};class StaticB
{
public:StaticB() { cout << "in StaticB()" << endl; }~StaticB() { cout << "in ~StaticB()" << endl; }
};class A
{
public:int a;int b = -1;C c;static StaticB sb; // 只是声明静态成员，并没有定义，也没有初始化。不占内存。static StaticA sa;static D d;
public:A() :b(0), a(b + 2) { cout << "in A()" << endl; }~A() { cout << "in ~A()" << endl; }void print(){cout << "a = " << a << " ,b = " << b << endl;}
};StaticB A::sb;
StaticA A::sa; // 这里才是定义,同时可以在这里初始化class E
{
public:E() { cout << "in E()" << endl; }~E() { cout << "in ~E()" << endl; }
};class F
{
public:F() { cout << "in F()" << endl; }~F() { cout << "in ~F()" << endl; }
};class B : public E, public A
{
public:B() { cout << "in B()" << endl; }~B() { cout << "in ~B()" << endl; }private:D d;static StaticB sb;
};StaticB B::sb;
D A::d;int main()
{cout << "test start" << endl;{B b;static F f;}cout << "test end" << endl;return 0;
}

output

in StaticB()
in StaticA()
in StaticB()
in D()
test start
in E()
in C()
in A()
in D()
in B()
in F()
in ~B()
in ~D()
in ~A()
in ~C()
in ~E()
test end
in ~F()
in ~D()
in ~StaticB()
in ~StaticA()
in ~StaticB()

其中