“没有合适的默认构造函数可用"--为什么甚至调用默认构造函数?

2021-12-30 00:00:00 constructor c++ member default-constructor

我已经查看了其他一些关于此的问题，但我不明白为什么在我的情况下甚至应该调用默认构造函数.我可以只提供一个默认构造函数，但我想了解它为什么这样做以及它会影响什么.

I've looked at a few other questions about this, but I don't see why a default constructor should even be called in my case. I could just provide a default constructor, but I want to understand why it is doing this and what it affects.

error C2512: 'CubeGeometry' : no appropriate default constructor available

我有一个名为 ProxyPiece 的类，其成员变量为 CubeGeometry.构造函数应该接收 CubeGeometry 并将其分配给成员变量.这是标题:

I have a class called ProxyPiece with a member variable of CubeGeometry.The constructor is supposed to take in a CubeGeometry and assign it to the member variable. Here is the header:

#pragma once
#include "CubeGeometry.h"

using namespace std;
class ProxyPiece
{
public:
    ProxyPiece(CubeGeometry& c);
    virtual ~ProxyPiece(void);
private:
    CubeGeometry cube;
};

和来源:

#include "StdAfx.h"
#include "ProxyPiece.h"

ProxyPiece::ProxyPiece(CubeGeometry& c)
{
    cube=c;
}


ProxyPiece::~ProxyPiece(void)
{
}

立方体几何的标题看起来像这样.使用默认构造函数对我来说没有意义.我还需要它吗?:

the header for cube geometry looks like this. It doesn't make sense to me to use a default constructor. Do I need it anyways?:

#pragma once
#include "Vector.h"
#include "Segment.h"
#include <vector>

using namespace std;

class CubeGeometry
{
public:
    CubeGeometry(Vector3 c, float l);

    virtual ~CubeGeometry(void);

    Segment* getSegments(){
        return segments;
    }

    Vector3* getCorners(){
        return corners;
    }

    float getLength(){
        return length;
    }

    void draw();

    Vector3 convertModelToTextureCoord (Vector3 modCoord) const;

    void setupCornersAndSegments();

private:
    //8 corners
    Vector3 corners[8];

    //and some segments
    Segment segments[12];

    Vector3 center;
    float length;
    float halfLength;
};

推荐答案

您的默认构造函数在此处隐式调用:

Your default constructor is implicitly called here:

ProxyPiece::ProxyPiece(CubeGeometry& c)
{
    cube=c;
}

你想要

ProxyPiece::ProxyPiece(CubeGeometry& c)
   :cube(c)
{
    
}

否则你的ctor相当于

Otherwise your ctor is equivalent to

ProxyPiece::ProxyPiece(CubeGeometry& c)
    :cube() //default ctor called here!
{
    cube.operator=(c); //a function call on an already initialized object
}

冒号后面的东西叫做成员初始化列表.

顺便说一句，我将参数作为 const CubeGeometry&c 而不是 CubeGeomety&c 如果我是你.

Incidentally, I would take the argument as const CubeGeometry& c instead of CubeGeomety& c if I were you.

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