在Qt中对vtable的未定义引用 [英] Undefined reference to vtable in Qt

问题描述

我收到虚拟表错误，而我无法检测到我的代码中的任何故障。有人能给我一个正确的方向点吗？对于荷兰语术语，抱歉，希望这不是问题。

I am getting a virtual table error while I can not detect any faults in my code. Could someone give me a point in the right direction? Sorry for the dutch terminology, hopefully it isn't an issue.

#ifndef LIJST_H
#define LIJST_H

#include "product.h"
#include <list>

typedef list<Product*> lijst;

#endif // LIJST_H

// Methode

#ifndef METHODE_H
#define METHODE_H

#include "lijst.h"

class Methode
{
public:
    Methode() {}
    virtual ~Methode() {}
    virtual double run(lijst *items);
};

#endif // METHODE_H

// Productmethode
#ifndef PRODUCTMETHODE_H
#define PRODUCTMETHODE_H

#include "methode.h"

class ProductMethode : public Methode
{
private:
    map<string,double> kortingsTabel;
public:
    ProductMethode() {}
    void addKorting(string naam, double korting);
    double run(lijst *items);
};

// Main
#include <QCoreApplication>
#include "factuur.h"
#include "product.h"
#include "globalemethode.h"
#include "productmethode.h"
#include "drempelmethode.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    GlobaleMethode G ( 0.1 );
    ProductMethode P;
    P.addKorting ( "Melk", 0.1 );
    P.addKorting ( "Boter", 0.05 );
    Factuur F ( &G );
    F.addProduct ( new Product ( "Melk", 0.75 ) );
    F.addProduct ( new Product ( "Kaas", 5 ) );
    F.addProduct ( new Product ( "Boter", 1.7 ) );
    cout << F.totaal ( ) << endl;
    F.setMethode ( &P );
    cout << F.totaal ( );

    return a.exec();
}

推荐答案

class Methode ：

virtual double run(lijst *items);

该方法也需要定义。只有纯虚拟函数才允许没有定义。

The method needs to be defined as well. Only pure virtual functions are allowed to be without a definition.

此外，通常使用 virtual 重载派生类的某些基类方法的行为，示例您不为覆盖的 virtual 方法提供定义。你应该。如果你不需要那么为什么你使方法 virtual 开始？不需要 virtual 。

Also, one would usually use virtual to overidde behavior of certain base class method for derived class, but in your example you do not provide a definition for the overidden virtual method. You should. If you don't need to then why did you make the method virtual to begin with? It need not be virtual.

：

这是什么意思，虚拟表是一个未解决的外部？

What does it mean that the "virtual table" is an unresolved external?

这篇关于在Qt中对vtable的未定义引用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！