继承的构造函数

1.单继承

#include"iostream"
using namespace std;

class Base {
public:
	int b;
	Base() { b=1; };
	Base(int b_) { b = b_; };
};

class Derive :public Base {
public:
	int d{0};
	Derive(int b_) :Base(b_){}	//没有这句Derive d(2)会报错
	Derive() = default;			//自动调用Base()构造b
};

int main() {
	Derive d1;
	Derive d2(2);
	cout << d1.b << endl;
	cout << d2.b << endl;
	
	return 0;
}

为什么继承构造函数需要using：https://www.runoob.com/w3cnote/cpp11-inheritance-constructor.html

2.多继承

#include<iostream>
using namespace std;

struct Base1
{
	Base1() = default;
	Base1(const string& s_) { s = s_; cout << "Base1" << endl; };
	string s;
};

struct Base2
{
	Base2() = default;
	Base2(const string& s_) { s = s_; cout << "Base2" << endl;
	};
	string s;
};

struct D1 :Base1, Base2 {
	//using Base1::Base1;
	//using Base2::Base2;	会有相同函数冲突
	D1(const string& s) :Base1(s), Base2(s) { cout << "D1" << endl; };
	D1() = default;
};

int main() {
	D1 d("hello");
	cout << d.Base1::s;
	return 0;
}