`QObject`子类和复制构造函数出错：`QObject::QObject(const QObject&)为private`

Question

下面的编译错误就是我所知道的：

/usr/lib/qt-3.3/include/qobject.h: In copy constructor Product::Product(const Product&):
/usr/lib/qt-3.3/include/qobject.h:211: error: QObject::QObject(const QObject&) is private
Product.h:20: error: within this context
HandleTCPClient.cpp: In member function int Handler::HandleTCPClient(int, std::string, std::string):
HandleTCPClient.cpp:574: note: synthesized method Product::Product(const Product&) first required here 
HandleTCPClient.cpp:574: error:   initializing argument 1 of std::string productDetails(Product)
/usr/lib/qt-3.3/include/qobject.h: In member function Product& Product::operator=(const Product&):
Product.h:20:   instantiated from void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = Product, _Alloc = std::allocator<Product>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_vector.h:610:   instantiated from âvoid std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = Product, _Alloc = std::allocator<Product>]â
HandleTCPClient.cpp:173:   instantiated from here
/usr/lib/qt-3.3/include/qobject.h:212: error: QObject& QObject::operator=(const QObject&) is private
Product.h:20: error: within this context
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/vector.tcc: In member function void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = Product, _Alloc = std::allocator<Product>]:
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/vector.tcc:260: note: synthesized method âProduct& Product::operator=(const Product&) first required here 
make: *** [HandleTCPClient.o] Error 1

我的HandleTCPClient.cpp线路574的一部分：

            Product tempProduct;// temporary Product storage variable
            tempProduct.setHandler(this);
...

            else if (output[1] == '5') // description
            {
                output.erase(0,2); // erase the sequence numbers
                tempProduct.description = output;
    LINE 574            output = productDetails(tempProduct); // obtain client given information about selling product
            }

产品.h：：

#include <string>
#include <qtimer.h>
#include "HandleTCPClient.h"
#ifndef PRODUCT_H
#define PRODUCT_H
#include <qobject.h>
#include <qgl.h>

class Handler;

//Define ourselves a product class
class Product : public QObject
    {

        Q_OBJECT

        void startTimer();

    public:
        Product();

        string seller, itemName, description, highestBidder;
        double price, min, buyingPrice, currentBid;
        int time;
        bool isSold;
        Handler *handler;

        void setHandler(Handler *h);

    public slots:
        void setProductToSold();

    };

#endif

Product.cpp:：

#include <string>
using std::string;

#include "Product.h"

Product::Product()
{
    seller = "";
    itemName = "";
    price = 0.00;
    min = 0.00;
    buyingPrice = 0.00;
    time = 0;
    description = "";
    highestBidder = "None";
    currentBid = 0.00;
}

void Product::setHandler(Handler *h)
{
    handler = h;
}

谢谢你的帮助=)

Answer 1

Product是QObject的子类，不能复制。您的代码试图将其复制到某个地方(可能是在productDetails(tempProduct)中)，这会导致错误。也许你可以通过const引用将它传递给你的函数；或者也许需要重新设计你的程序。

您的编译器告诉您QObject的复制构造函数是私有的，因此它不能被任何不是基类方法的函数调用。Qt就是这样设计的。

Qt禁止复制QObjects的一个原因是它管理QObject的子代的内存。当一个QObject被删除时，它的所有子项也会被删除。如果QObject是可复制的，这将是不切实际的。

Answer 2

QObject子体不允许复制...

请参阅http://lists.trolltech.com/qt-interest/2001-02/thread00123-0.html

您的productDetails()函数通过值接受其参数，因此需要进行一次复制。将其更改为采用常量引用。

Answer 3

在第574行，您正在尝试将其中一项传递给productDetails函数。你没有显示它，但是我想这个函数要么接受一个值。所以编译器试图创建一个全新的对象来传递它，但这是库不允许的，它故意将复制构造函数设置为私有。

显式创建一个新对象，或者修复被调用的函数。