如何使用好友类c ++ [英] How to use friend class c++

问题描述

我有一个带有朋友点类的矩形类。我使用笛卡尔坐标，所以我将在矩形类中有四个点。点在点类中定义。当在源文件中定义矩形构造函数时，得到错误（在注释中标记）：

I have a rectangle class with a friend point class. I am using cartesian coordinates, so I will have four points in the rectangle class. The points are defined in the point class. When defining the rectangle constructor in the source file, I get the error(marked in comment):

矩形没有成员Rectangle

Rectangle has no member Rectangle

标题：

using namespace std;

class Rectangle
{
public:
    Rectangle(Point, Point, Point, Point);
    friend class Point;
    ~Rectangle();
private:
    Point a;
    Point b;
    Point c;
    Point d;
};

class Point
{
public:
    Point(int, int);
private:
    int x;
    int y;
};

来源：

Rectangle::Rectangle(Point v1, Point v2, Point v3, Point v4)    //error here
{

}

Point::Point(int value1, int value2)
{
    if (x <= 20 && y <= 20){
        x = value1;
        y = value2;
    }
    else{
        throw invalid_argument("");
    }
}

推荐答案

您的构造函数声明中的星号。

Remove the asterisks in your constructor declaration.

向前声明Point或在Rectangle之前声明Point。

Either forward declare Point, or declare Point before Rectangle.

真的不应该在头文件中使用using namespace。

You also really shouldn't use "using namespace" inside of a header file.

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