我如何使用C ++中的继承函数访问派生类中的局部变量

问题描述 投票:0回答:1

如何使用基类/继承类的成员函数访问派生类的局部变量?

我从JavaScript的角度来看,虽然我有一些Java经验,但已经有一段时间了。这是JavaScript所需的结果。

// JavaScript Example

class State {
    constructor(name){
        this.name = name || "Parent";
    }

    getName(){ return this.name };
}

class StateReading extends State {
    constructor(){
        super("Child");
    }

    // Since StateReading extends State, it also inherits its parent's functions
    // in this case, it inherits getName()

}

const s = new StateReading();
console.log(s.getName());   // I print out "Child"

[我正在尝试开发与C ++类似的东西,但是正忙着时间让所有部分(har har)对齐。

#include <iostream>
using namespace std;


 class State {
    std::string name = "Parent";

    public: 
        virtual std::string getName() {  // "virtual" keywords removes the compile time linkage
            return name;
        }
 };

 class StateReading : public State {
     std::string name = "Child";
 };


int main() {

    StateReading sr = StateReading();
    State* s = &sr;  // Make state a pointer to a memory address so it can be reused

    cout<<s -> getName(); // Prints "Parent" ... but I'm pointing to StateReading's memory address ... :/
    cout<<sr.getName(); // At least this one should be child ... wait, it's "Parent" too?!
    return 0;
}

我可以使它起作用的唯一方法是在子类中重写getName()。但是我真的不想覆盖子类中的每个方法。我正在尝试使用具有工厂模式的多态性概念。我知道我总是会创建某种“状态”,但是它可以是许多派生类中的任何一个。

// Untested example
class StateFactory{

  public: 
    static make(params){
        switch(params) {
            case 0: return StateReading();
            case 1: return StatePaused();
            case 2: return StateWriting();
            default: // etc.
        }
    }
}


State state = StateFactory.make(params);
state.getName();  // prints out the state's name.  

对此有何想法?似乎必须重写每个派生类才能获取本地实例变量,这将是真正的维护噩梦。

c++ inheritance polymorphism
1个回答
0
投票

在JS中,您称为基类的构造函数。在C ++中执行相同的操作]

#include <iostream>
using namespace std;


 class State {
    std::string name = "Parent";

    public: 
        std::string getName() {
            return name;
        }
 };

 class StateReading : public State {
     StateReading() : State("Child"){}
 };


int main() {

    StateReading sr = StateReading();
    State* s = &sr;  // Make state a pointer to a memory address so it can be reused

    cout<<s -> getName(); // Prints "Parent" ... but I'm pointing to StateReading's memory address ... :/
    cout<<sr.getName(); // At least this one should be child ... wait, it's "Parent" too?!
    return 0;
}

您不需要virtual,因为您没有覆盖任何内容。

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