Question

我正在从子类中的父类实现纯虚函数。

当我尝试在eclipse中实例化子类时，它说

'derived'类型必须实现继承的纯虚方法'Base :: compareTo'

我很确定我这样做了。我的基类是..

base.h

#ifndef BASE_H_
#define BASE

class Base{
public:
    Base();
    virtual ~Base();
    virtual int compareTo(void* compare)=0;
};

#endif /* BASE*/

然后我的derived.h

#ifndef DERIVED_H_
#define DERIVED_H_
#include "Base.h"

class Derived : public Base {

public:
    int x;
    Derived(int y);
    virtual ~Derived();
    int compareTo(void* compare);

};

#endif /* DERIVED_H_ */

Derived.cpp

#include "Derived.h"
#include "Base.h"

Derived::Derived(int y) {
    // TODO Auto-generated constructor stub
        x=y;
}

Derived::~Derived() {
    // TODO Auto-generated destructor stub
}

int Derived::compareTo(void* compare) {

    Derived* compared;
    int result=0;

    if(compared=dynamic_cast<Derived*>(compare))
    {
        if(x<compared->x)
        {
            result=-1;
        }
        else
        {
            result=1;
        }
    }

    return result;

}

Answer 1

我假设此消息来自eclipses代码分析器，而不是来自编译器。代码分析器是错误的，你是对的。您已在Derived中的基类中正确实现了纯虚方法。如果您尝试实例化Derived，则代码应该编译。

您的CDT版本可能低于8.2.1吗？如果是这样，您可能会遇到this bug，应该在8.2.1中修复。

但是您的代码中还有另一个错误。你不能dynamic_cast一个void指针。

Answer 2

尝试这个基类代码：

#ifndef BASE_H_
#define BASE_H_

class Base{
public:
    //Base (); not needed in the virtual class
    virtual ~Base() {};
    virtual int compareTo(void* compare)=0;
};

#endif /* BASE*/

#ifndef DERIVED_H_
#define DERIVED_H_
#include "Base.h"

class Derived : public Base {

public:
    int x;
    Derived(int y);
    virtual ~Derived();
    int compareTo(void* compare) override/*C++11*/;
};

#endif /* DERIVED_H_ */

#include "Derived.h"
//#include "Base.h" Not needed

Derived::Derived(int y) {
    // TODO Auto-generated constructor stub
        x=y;
}

Derived::~Derived() {
    // TODO Auto-generated destructor stub
}

int Derived::compareTo(void* compare) {

    Derived* compared;
    int result=0;

    if(compared=dynamic_cast<Derived*>(compare))
    {
        if(x<compared->x)
        {
            result=-1;
        }
        else
        {
            result=1;
        }
    }

    return result;

}

在子类中实现纯虚方法

2 个答案: