C++中构造函数的初始化顺序说明

#include <iostream>
using namespace std;
 
class A{
  public:
    A ():m_iVal(0){test();}//这里的test会调用父类的virtual void func()
    virtual void func() { std::cout<<m_iVal<<' ';}
    void test(){func();}
  public:
      int m_iVal;
};
class B : public A{
  public:
    B(){test();}//这里的test会调用父类的test()进而通过指针匹配
    virtual void func(){
      ++m_iVal;
      std::cout << m_iVal << ' ';
      }
};
int main(int argc ,char* argv[]){
  A*p = new B;
  p->test();
  return 0;
}

#include<iostream>
using namespace std;

class MyClass {
public:
    MyClass(int i = 0) { // 构造函数
        cout << i;
    }
    MyClass(const MyClass &x) { // 拷贝构造函数
        cout << 2;
    }
    MyClass &operator=(const MyClass &x) { // 赋值运算符
        cout << 3;
        return *this;
    }
    ~MyClass() { // 析构函数
        cout << 4;
    }
};

int main() {
    MyClass obj1(1), obj2(2); // 创建 obj1 和 obj2
    MyClass obj3 = obj1;      // 创建 obj3 并初始化
    return 0;
}

MyClass obj3 = obj1;

MyClass obj3; // 先默认构造
obj3 = obj1; // 再赋值

#include <iostream>
class Base {
public:
    void foo() { // 非虚函数
        std::cout << "Base::foo()" << std::endl;
    }
};

class Derived : public Base {
public:
    virtual void foo() { // 子类声明为虚函数
        std::cout << "Derived::foo()" << std::endl;
    }
};

class GrandDerived : public Derived {
public:
    void foo() { // 重写 Derived 中的虚函数
        std::cout << "GrandDerived::foo()" << std::endl;
    }
};

int main() {
    Base* b1 = new Derived();
    b1->foo(); // 输出 "Base::foo()"

    Derived* d1 = new Derived();
    d1->foo(); // 输出 "Derived::foo()"

    Base* b2 = new GrandDerived();
    b2->foo(); // 输出 "Base::foo()"

    Derived* d2 = new GrandDerived();
    d2->foo(); // 输出 "GrandDerived::foo()"
    delete b1; delete d1; delete b2; delete d2;
    return 0;
}