错误消息:使用复制构造函数和重载赋值运算符

Error messages: with Copy constructor and Overloaded assignment operator

本文关键字：构造函数 重载 赋值运算符 复制 消息 错误      更新时间：2023-10-16

这是我之前问过的问题。我在使用论坛建议的复制构造函数时遇到编译错误。

class A
{
private:
    int a;
    int b;

public:
    A() { a = 0; b = 0; }
    int getA() { return a; }
    int getB() { return b; }
    A(const Beta& b) :a{ *b.X() }, b{ *b.Y } {} 
};
class Beta
{
private:
    int *x;
    int *y;
public:
    Beta(int a, int b) { x =&a; y = &b; }
    int* X() { return x; }
    int* Y() { return y; }
};
int main()
{
    B aObject;
    Alpha a1 = aBObject;
    Alpha a2;
    a2 = aBObject;
    return 0;
}

在复制构造函数参数中没有 const Alpha(Beta&be(

Error   C2061   syntax error: identifier 'Beta' 
Error   C2228   left of '.getY' must have class/struct/union 
Error   C2228   left of '.getX' must have class/struct/union 
Error   C2679   binary '=': no operator found which takes a right-hand operand of type 'Beta' (or there is no acceptable conversion)
Error   C2440   'initializing': cannot convert from 'Beta' to 'Alpha' 
Error   C2065   'be': undeclared identifier 
Error   C2535   'Alpha::Alpha(void)': member function already defined or declared

在复制构造函数参数中使用 const Alpha(const Beta&be(

Error (active)  the object has type qualifiers that are not compatible with the member function "Beta::getX" 
Error (active)  the object has type qualifiers that are not compatible with the member function "Beta::getY" 
Error   C2061   syntax error: identifier 'Beta' 
Error   C2228   left of '.getY' must have class/struct/union 
Error   C2228   left of '.getX' must have class/struct/union 
Error   C2679   binary '=': no operator found which takes a right-hand operand of type 'Beta' (or there is no acceptable conversion)
Error   C2440   'initializing': cannot convert from 'Beta' to 'Alpha' 
Error   C2065   'be': undeclared identifier 
Error   C2535   'Alpha::Alpha(void)': member function already defined or declared

这是你想要的吗？

class Beta
{
private:
    int *x;
    int *y;
public:
    Beta() { x = nullptr; y = nullptr; }
    int* getX() { return x; }
    int* getY() { return y; }
};
class Alpha
{
private:
    int a;
    int b;

public:
    Alpha() { a = 0; b = 0; }
    int getA() { return a; }
    int getB() { return b; }
    Alpha( Beta& be) :a{ *be.getX() }, b{ *be.getY() } {} 
//It is not copy Constructor. You can't pass const reference here because getX getY returns pointer. So it could break const contract
};

int main()
{
    Beta aBetaObject;
    Alpha a1 = aBetaObject;
    Alpha a2;
    a2 = aBetaObject;
    return 0;
}

代码中没有复制构造函数(或赋值运算符(。但无论如何，这不是问题所在。它们发出您的代码Alpha使用Beta Beta之前发出问题。这就是编译器所抱怨的，它在你第一次使用它时无法识别Beta。

只需移动Beta，使其定义在Alpha之前，一切都将编译。

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