Question

为什么类TB在以下代码中是抽象的？

#include <stdio.h>

struct IA
{
    virtual long X() = 0;
};
struct IB: public IA
{
    virtual long Y() = 0;
};

struct TA: public IA
{
    virtual long X() { return 5; };
};

struct TB: public IB, public TA
{
   // virtual long X() { return TA:: X(); };
    virtual long Y() { return 7; };
};

int main()
{
    TB b;
}


main.cpp:25: error: cannot declare variable 'b' to be of abstract type 'TB'
     TB b;

Answer 1

问题是TB从IA继承两次，因为IA是IB和TA的父级。要解决此问题，您需要重新设计类层次结构或使用virtual inheritance：

#include <stdio.h>

struct IA
{
    virtual long X() = 0;
};
struct IB: public virtual IA // virtual inheritance here
{
    virtual long Y() = 0;
};

struct TA: public virtual IA // and here
{
    virtual long X() { return 5; };
};

struct TB: public IB, public TA
{
   // virtual long X() { return TA:: X(); };
    virtual long Y() { return 7; };
};

int main()
{
    TB b;
}

派生类仍然是抽象的

1 个答案: