c++ - 我们如何使用委托(delegate)构造函数从派生类调用基类构造函数

Question

我知道并且我已经阅读了很多从派生类调用基类构造函数的线程，但我想使用委托(delegate)构造函数来实现它

这是我的代码

错误状态

“委托(delegate)构造函数不能有其他内存初始化器”

#include <iostream>
using namespace std;

// Shivang101
class Base
{
private:
    int value;

public:
    Base() : value{0}
    {
        cout << "Base no args constructor called" << endl;
    }
    Base(int x) : value{x}
    {
        cout << "Base (int) overloaded constructor called" << endl;
    }
    ~Base()
    {
        cout << "Base Destructor called" << endl;
    }
};
class Derived : public Base
{

private:
    int testing_value;
    int doubled_value;
    // using Base ::Base;

public:
    Derived() : Derived{0, 0}
    {
        cout << "NO arg constructor called" << endl;
    };
    // In the below line I'm Trying a call the base class constructor but getting error
    Derived(int testing_val) : Base{testing_val}, Derived{testing_val, 0}
    {
        cout << "One arg constructor called" << endl;
    }
    
    Derived(int testing_val, int doubled_val) : testing_value{testing_val}, doubled_value{doubled_val}
    {
        cout << "Delegating constructor/ overloaded called" << endl;
    }
    ~Derived()
    {
        cout << "Derived destructor called" << endl;
    }
};
int main()
{
    Derived d{1000};
    return 0;
}

我想调用我的基类构造函数并将Base类中的“值”初始化为“1000”，并初始化中的“testing_*value”和“doubled_*value”派生类分别为“1000”和“2000”

Answer 1

构造函数负责初始化所有成员和基本子对象。

委托(delegate)构造函数委托(delegate)给不同的构造函数。

不可能两者兼而有之。要么委托(delegate)其他地方，要么初始化成员和基础子对象。

引用自cppreference :

Delegating constructor

If the name of the class itself appears as class-or-identifier in the member initializer list, then the list must consist of that one member initializer only; such a constructor is known as the delegating constructor, and the constructor selected by the only member of the initializer list is the target constructor

我想你可以重新排列构造函数以达到预期的效果。虽然我不知道如何在不实现另一个构造函数或更改委托(delegate)方式的情况下完成此操作，因为目前采用两个参数的构造函数调用 Base 的默认构造函数，但委托(delegate)给它的构造函数尝试调用Base{testing_val}<​​。