C++派生类链构造函数错误

Question

全部，

我在继承链中有 3 个类(在 C++ 中)，每个类都设置了默认的基本构造函数。但是，链中的第 3 类提示第 1 类没有匹配的构造函数。下面是构造函数的代码:

class Base
{
    protected:
        int a, b;
    public:
        Base::Base(int first, int second)
        {
            this->a = first;
            this->b = second;
        }
}

class Second : protected Base
{
    protected:
        int c;
    public:
        Second::Second(int first, int second, int third = 2) : Base(first, second)
        {
            this->c = third;
        }
}

class Final : protected Second
{
    private:
        int d;
    public:
        Final::Final(int first, int second, int third = 2) : Second(first, second, third)
        {
        }
}

编译时报错

“在构造函数中 Final::Final(int first, int second, int third)

没有对 Base() 的匹配调用"

为什么尝试调用 Base() 而不是 Base(first, second)？

Answer 1

这可能对您有所帮助，这就是我构建此类层次结构的方式。

class Base {
protected: 
    int m_a, m_b;

public:
    Base( int first, int second );
    virtual ~Base(){}
};

Base::Base( int first, int second ) :
m_a( first ),
m_b( second ) 
{}

class Second : protected Base {
protected:
    int m_c;
public:
    Second( int first, int second, int third = 2 );
    virtual ~Second(){}
};

Second::Second( int first, int second, int third ) :
Base( first, second ),
m_c( third )
{}

class Final : protected Second {
private:
    int m_d;
public:
   Final( int first, int second, int third = 2 );
   virtual ~Final(){}
};

Final::Final( int first, int second, int third ) :
Second( first, second, third )
{}

如果你想将你的定义保留在类中而不是在类声明之外定义它们，那么试试这个

class Base {
protected: 
    int m_a, m_b;

public:
    Base( int first, int second ) : m_a( first ), m_b( second ) {}
    virtual ~Base(){}
};

class Second : protected Base {
protected:
    int m_c;
public:
    Second( int first, int second, int third = 2 ) : 
    Base( first, second ),
    m_c( third ) {}

    virtual ~Second(){}
};

class Final : protected Second {
private:
    int m_d;
public:
   Final( int first, int second, int third = 2 ) :
   Second( first, second, third ) {}

   virtual ~Final(){}
};

在使用继承时，最好确保将析构函数声明为虚拟的。如果在类外部定义构造函数或函数，则只需要使用类作用域解析运算符，而要设置基本成员变量则不需要使用 this-> 指针运算符，可以像我一样使用初始化列表已在定义构造函数时显示。