为什么要使用虚拟析构函数? [英] Why virtual destructor?

问题描述

我正在检查一些代码，计划对其进行调整以适合我的研究.因此头文件看起来像这样

I am going through some code,plan to adapt it for my research.So header file looks like this

#ifndef SPECTRALCLUSTERING_H_
#define SPECTRALCLUSTERING_H_

#include <vector>
#include <eigen3/Eigen/Core>

class SpectralClustering {
public:
    SpectralClustering(Eigen::MatrixXd& data, int numDims);
    virtual ~SpectralClustering();

    std::vector<std::vector<int> > clusterRotate();
    std::vector<std::vector<int> > clusterKmeans(int numClusters);
    int getNumClusters();

protected:
    int mNumDims;
    Eigen::MatrixXd mEigenVectors;
    int mNumClusters;
};

#endif /* SPECTRALCLUSTERING_H_ */

后面的主要代码

#include "SpectralClustering.h"
#include <eigen3/Eigen/QR>

SpectralClustering::SpectralClustering(Eigen::MatrixXd& data, int numDims):
    mNumDims(numDims),
    mNumClusters(0)

所以我不明白为什么在.h文件中使用虚拟析构函数.从此中，我们可以了解到，当您可以删除虚拟实例的实例时，虚拟析构函数非常有用.通过指向基类的指针派生的类.但是我认为这段代码不是这种情况.有人可以解释所有这些吗?

So I do not understand why virtual destructor was used in the .h file. From this we can learn that virtual destructors are useful when you can delete an instance of a derived class through a pointer to base class.But I think this is not case with this code.Can someone explain all this?

推荐答案

将析构函数设为虚拟的原因是，您计划将该类进行多态继承和使用.如果我们有

The reason you would make a destructor virtual is that you plan for that class to be inherited and used polymorphicly. If we had

class Foo {};
class Bar : public Foo {};

Foo * f = new Bar();
delete f; // f's destructor is called here

将调用Foo的析构函数，并且对象的Bar部分的任何成员都不会被销毁.如果Foo具有虚拟析构函数，则将执行vtable查找，而将调用Bar析构函数，而不是正确地破坏对象.

The destructor for Foo would be called and no members of the Bar part of the object would be destroyed. If Foo had a virtual destructor then a vtable lookup would happen the the Bar destructor would be called instead correctly destroying the object.

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