C++ 派生类仅使用继承的基构造函数的一部分

Question

I am certain that this is a basic question but I have not been able to find the answer anywhere. Let's say I have a base class with constructor:

class Parent{
public:
    double propertyA, propertyB;
    Parent(double propertyA, double propertyB){
        this->propertyA = propertyA;
        this->propertyB = propertyB;
}
};

and then I want a derived class to use this base constructor but it will only need to take in propertyB . propertyA will end up being a constant (let's say 1.0 ).

Currently I am trying:

class Child : public Parent {
public:
    Child(double PropertyB): Parent(1.0, PropertyB) {}
};

I am not certain that this behaves as I want it to though. Is this how I should be doing this?

Answer 1

The only way to be sure is to test, I think:

#include <iostream>

class Parent
{
public:
    double propertyA, propertyB;
    Parent(double propertyA, double propertyB)
    {
        this->propertyA = propertyA;
        this->propertyB = propertyB;
    }
};
class Child : public Parent
{
public:
    Child(double PropertyB): Parent(1.0, PropertyB) {}
    double getPropertyA()
    {
        return propertyA;
    }
    double getPropertyB()
    {
        return propertyB;
    }
};

int main()
{
    double a = 3.0;
    double b = 5.0;
    Parent* parent = new Parent(a,b);
    Child* child = new Child(b);
    std::cout << "PropertyA for child " << child->getPropertyA();
}

The output is:

1 

Answer 2

You can simply overload the constructor. Code should be like this -

class Parent{
public:
    double propertyA, propertyB;
    Parent(double propertyA, double propertyB){
        this->propertyA = propertyA;
        this->propertyB = propertyB;
    }
    Parent(double propertyB){ 
        this->propertyA = 1.0; // constant value
        this->propertyB = propertyB;
    }
};
class Child : public Parent {
public:
    Child(double PropertyB): Parent(PropertyB) {

    }
};