类构造函数参数C ++ [英] Class Constructor arguments C++

问题描述

我正在为x和y笛卡尔坐标系创建一个pair1类. x和y是双精度.我需要3个构造函数.

I am creating a pair1 class for a x and y Cartesian coordinate system. x and y are doubles. I need to have 3 constructors.

1. 没有参数，默认将x和y设置为零.
2. 一个论点将x赋值，默认y为零.
3. 一个分会默认将x设置为零，并指定y.我不确定是否要正确设置课程.我收到以下错误:pair1::pair1(double)和pair1::pair1(double)无法重载.

1. No arguments, defaults x and y to zero.
2. One arguement assigns x and defaults y to zero.
3. One arugeument defaults x to zero and assigns y. I'm not sure if I am setting up the class right. I get the follwing error: pair1::pair1(double) and pair1::pair1(double) cannot be overloaded.

我的课:

class pair1
{
private:
    double x;
    double y;

public:
    pair1(){ x = 0.0, y = 0.0; }    
    pair1( double a ){ x = a; y =0.0; }
    pair1(double b){ x = 0.0;  y = b; }
};

推荐答案

1)没有参数，默认将x和y设置为 零.

1) no arguments, defaults x and y to zero.

那很容易

2)一个论点分配x并且 默认将y设置为零.

2) one arguement assigns x and defaults y to zero.

3)一副 默认将x设置为零，并指定y.

3) one arugeument defaults x to zero and assigns y.

这是一个问题.您怎么知道，当您只有一个参数时，这两个参数中的哪一个将被调用?这就是为什么您会收到编译错误的原因.

That's a problem. How do you know, when you only have one parameter, which of the two is meant to be called? That's why you get a compilation error.

相反-如果需要，请使用默认构造函数(无参数的构造函数)，完整构造函数(无参数的构造函数)和SetX()和SetY()分别设置X和Y，并通过函数的名称.

Instead - use the default constructor (the one with no parameters), full constructor (the one with both), if needed, and SetX() and SetY() to set the X and Y separately, and make distinction by the name of the function.

class pair1
{
    private:
    double x;
    double y;

    public:
    pair1( double a=0.0, double b=0.0 ){ x = a; y =b; };
                     // default value 0.0 allows to only
                     // set x, and leave y to be the default,
                     // or leave them both default.
    void SetX(double a) { x=a;};
    void SetY(double b) { y=b;};
};

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