标签: copy-constructor

我正在尝试初始化一个对象数组:

SinglyLinkedList offeredClasses[22] = {SinglyLinkedList("CSCE101"),SinglyLinkedList("CSCE101L"),SinglyLinkedList("CSCE150E"),SinglyLinkedList("CSCE150EL"),SinglyLinkedList("CSCE150EM"),SinglyLinkedList("CSCE150EML"),SinglyLinkedList("CSCE155"),SinglyLinkedList("CSCE155H"),SinglyLinkedList("CSCE156"),SinglyLinkedList("CSCE230"),SinglyLinkedList("CSCE230L"),SinglyLinkedList("CSCE235"),SinglyLinkedList("CSCE251"),SinglyLinkedList("CSCE310"),SinglyLinkedList("CSCE322"),SinglyLinkedList("CSCE361"),SinglyLinkedList("CSCE351"),SinglyLinkedList("CSCE451"),SinglyLinkedList("CSCE423"),SinglyLinkedList("CSCE428"),SinglyLinkedList("CSCE486"),SinglyLinkedList("CSCE487")};

但是当我尝试这样做时,它一直试图调用我的复制构造函数而不是重载的构造函数.有什么想法解决这个问题？

有问题的2个构造函数是:

SinglyLinkedList(string course); //Constructor
SinglyLinkedList(SinglyLinkedList & otherObj); //Copy Constructor

我需要复制构造函数用于其他事情,所以我不能删除它.

谢谢你的帮助!

这是程序......

class CopyCon
{
public:
char *name;

CopyCon()
{ 
    name = new char; 
}

CopyCon(const CopyCon &objCopyCon)
{
    name = new char;
    _tcscpy(name,objCopyCon.name);
}

~CopyCon()
{
    if( name != NULL )
    {
        delete name;
        name = NULL;
    }
}
};

int main()
{
    CopyCon objCopyCon1;
    objCopyCon1.name = "Hai";
    CopyCon objCopyCon2(objCopyCon1);
    objCopyCon1.name = "Hello";
    cout<<objCopyCon2.name<<endl;
    return 0;
}

一旦代码执行完成,当析构函数调用时,它会在'delete'上崩溃说...

调试错误!

计划:......

HEAP CORRUPTION DETECTED:在正常块(#124)之后的0x00366990.CRT检测到应用程序在堆缓冲区结束后写入内存.

(按"重试"调试应用程序)

我们不必在析构函数中清除堆内存.这个程序有什么问题？请帮忙!复制构造函数按预期完美地工作.但还是......!？

那么为什么不能在“ const Integer operator +（const Integer＆rv） ”函数中调用Copy构造函数。是因为RVO。如果是，我需要采取什么措施来防止这种情况发生？

#include <iostream>

using namespace std;

class Integer {
    int i;

public:
    Integer(int ii = 0) : i(ii) {
        cout << "Integer()" << endl;
    }

    Integer(const Integer &I) {
        cout << "Integer(const Integer &)" << endl;
    }

    ~Integer() {
        cout << "~Integer()" << endl;
    }

    const Integer operator+(const Integer &rv) const {
        cout << "operator+" << endl;
        Integer I(i + rv.i);
        I.print();
        return I;
    }

    Integer &operator+=(const Integer &rv) {
        cout << "operator+=" …

可能重复:
为什么在这种情况下不调用复制构造函数？

在下面的代码中,我构造了三个变量a1,a2和a3.

C++ Primer p.476中有一个例子:

string empty_copy = string();//copy-initialization

有没有人可以帮我解释一下

1)为什么a1和a2不是由复制构造函数构造的

2)我的代码中的初始化a2和书中的empty_copy有什么区别？

非常感谢!

#include<iostream>
using namespace std;
class A{
public:
    A(){}
    A(int v){}
    A(const A&x){
        cout<<"copy constructor"<<endl;
    }
};
A generateA(){
    return A(0);
}
int main(){
        cout<<"First:"<<endl;
        A a1=generateA();

        cout<<"Second:"<<endl;
        A a2=A(0);

        cout<<"Third:"<<endl;
        A a3=a1;
    return 0;
}

输出是(在Win7中的Visual Studio 2010和Ubuntu10.10中的g ++):

First:
Second:
Third:
copy constructor

可能重复:
如何为成员使用非默认构造函数？

我有当前的代码:

class ImagePoint {
private:
    int row;
    int col;

public:
    ImagePoint(int row, int col){
        this->row = row;
        this->col = col;
    }

    int get_row(){
        return this->row;
    }

    int get_col(){
        return this->col;
    }
};

我想这样做:

class TrainingDataPoint{
private:
    ImagePoint point;
public:
    TrainingDataPoint(ImagePoint image_point){
        this->point = image_point;
    }
};

但是这不会编译,因为该行ImagePoint point;要求ImagePoint类具有空构造函数.替代方案(从我读过的)说我应该使用指针:

class TrainingDataPoint{
private:
    ImagePoint * point;
public:
    TrainingDataPoint(ImagePoint image_point){
        this->point = &image_point;
    }
};

但是,一旦构造函数完成运行,此指针是否指向已清除的对象？如果是的话,我是否必须复制一份image_point？这需要复制构造函数吗？

我有这样的结构:

/* Renderable definition */
    struct Renderable
    {
        Renderable(VertexBufferPtr vertexBuffer, const Mat4& wvpMatrix, const Mat4& worldMatrix, const Vec4& diffuseColor, const float specularFactor) : 
                    mVertexBuffer(vertexBuffer), mTransform(wvpMatrix, worldMatrix), mMaterial(diffuseColor, specularFactor)
        {
        }

        /* Transform definition */
        struct Transform
        {
            Transform(const Mat4& wvpMatrix, const Mat4& worldMatrix) : mWVPMatrix(wvpMatrix), mWorldMatrix(worldMatrix)
            {
            }

            const Mat4 mWVPMatrix;
            const Mat4 mWorldMatrix; 
        };

        /* Material definition */
        struct Material
        {
            Material(const Vec4& diffuseColor, const float specularFactor) : mDiffuseColor(diffuseColor), mSpecularFactor(specularFactor)
            {
            }

            const Vec4 mDiffuseColor;
            const float mSpecularFactor;
        }; …

我写了一个程序如下:

#include <iostream>

using namespace std;

class A {
public:
    A() {
    }
    A(A &a) {
        id = a.id;
        cout << "copy constructor" << endl;
    }
    A& operator=(A &other) {
        id = other.id;
        cout << "copy assignment" << endl;
        return *this;
    }
    A(A &&other) {
        id = other.id;
        cout << "move constructor" << endl;
    }
    A& operator=(A &&other) {
        id = other.id;
        cout << "move assignment" << endl;
        return *this;
    }
public:
    int id = 10;
};

A foo() { …

请考虑以下代码:

#include <iostream>

struct A
{
    A() {} // Can't be commented
    A( const A& other ) =delete;
    int i;
};

struct B : public A
{
    B( int j ) { this->i = j; }
    B( const B& other ) { this->i = other.i; }
};

int main()
{
    B b(42);
    std::cout << b.i << std::endl;
}

如果我注释A的空构造函数,为什么我不能编译这段代码？我以为A总是有一个默认的构造函数,当我禁用它的复制构造函数时会发生什么变化？

将项目从Qt4迁移到Qt5我得到了这个错误,我已经研究过,显然你不能从QObject创建一个派生类的复制构造函数(这是不可思议的,因为这段代码不是我的,它应该在以前的版本中编译).复制构造函数并不真正复制任何QObject值,我不知道QList thingy有什么问题.

In file included from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include/QtGui/qwindowdefs.h:45:0,
                 from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include\QtWidgets/qwidget.h:45,
                 from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include\QtWidgets/QWidget:1,
                 from ..\marssies\wavingwidget.h:4,
                 from ..\marssies\wavingwidget.cpp:1:
..\marssies\graphicsprimitive.h: In instantiation of 'void QList<T>::node_construct(QList<T>::Node*, const T&) [with T = SIZArrow]':
..\..\..\..\..\Qt5\5.2.1\mingw48_32\include/QtCore/qlist.h:515:32:   required from 'void QList<T>::append(const T&) [with T = SIZArrow]'
..\..\..\..\..\Qt5\5.2.1\mingw48_32\include/QtCore/qlist.h:301:49:   required from 'void QList<T>::push_back(const T&) [with T = SIZArrow]'
..\marssies\wavingwidget.cpp:345:23:   required from here
In file included from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include/QtGui/qwindowdefs.h:45:0,
                     from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include\QtWidgets/qwidget.h:45,
                     from ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include\QtWidgets/QWidget:1,
                     from ..\marssies\wavingwidget.h:4,
                     from ..\marssies\wavingwidget.cpp:1:
    ..\marssies\graphicsprimitive.h: In instantiation of 'void QList<T>::node_construct(QList<T>::Node*, const T&) [with T = SIZPolygon]':
    ..\..\..\..\..\Qt5\5.2.1\mingw48_32\include/QtCore/qlist.h:515:32:   required from 'void …

有一些宏可以防止类被复制,例如: 宏禁止类复制和赋值.谷歌-vs- Qt

仅仅通过在我班级中使用unique_ptr,我会获得相同的结果吗？如果是这样,有没有理由不这样做？例如

class Foo {
  private:
    std::unique_ptr<int> DISABLE_COPY;
};