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我试图了解实现复制赋值运算符的正确方法=。所以我实现了这个例子：

class Window {
public:
    Window(const std::string& = std::string());

    Window(const Window&);
    Window& operator=(const Window&);
    ~Window();

    std::string win_name()const { return *psWinName; }
    std::size_t win_id()const { return winID; }

private:
    std::string* psWinName =  nullptr;
    std::size_t winID;
};

Window::Window(const std::string& win_name) : 
    psWinName(new std::string(win_name)),
        winID(0) {
}

Window::Window(const Window& rhs) :
    psWinName(new std::string(*rhs.psWinName)),
    winID(rhs.winID) {
}


/* Erroneous copy-assignment operator
Window& Window::operator=(const Window& rhs)
{
    delete psWinName;
    psWinName = new std::string(*rhs.psWinName);;
    winID = rhs.winID;

    return *this;
}
*/

Window& Window::operator=(const Window& rhs)
{
    std::string* tmp = new std::string(*rhs.psWinName);
    delete psWinName;
    psWinName = tmp;
    winID = rhs.winID;

    return *this;
}

Window::~Window() 
{
    delete psWinName;
}

int main() 
{

    /*Window win_explorer("Explorer");
    auto win_exp2(win_explorer);
    Window win_desktop("Desktop Window");

    Window win;
    win = win_desktop;

    win = win;

    cout << win_explorer.win_name() << " : " << win_explorer.win_id() << endl;
    cout << win_exp2.win_name() << " : " << win_exp2.win_id() << endl;
    cout << win_desktop.win_name() << " : " << win_desktop.win_id() << endl;
    cout << win.win_name() << " : " << win.win_id() << endl;*/

    int* p = new int(9);
    cout << p << " " << *p << endl;

    int* tmp = p;
    cout << tmp << " " << *tmp << endl;
    delete p;
    p = new int(*tmp);

    cout << p << " " << *p << endl;
    cout << tmp << " " << *tmp << endl;


    cout << "\ndone\n";
}

到目前为止，我已经展示了不正确的=运算符形式。

是不是错了，因为：

delete psName;
psName = new std::string(*rhs.psName); // UB here?

  • 所以我不知道这里的评估顺序是如何发生的：psName = new std::string(*rhs.psName);. 那么这是一个UB吗？

  • 还有呢：

    delete psName;
psName = new std::string();
*psName = *rhs.psName;

但是会产生相同的结果，即未定义的值。

  • 我谈论将一些对象分配给自身。

** 人们也争论：delete psName; psName = new std::string();他们说new可能会扔。但我认为只要我发布了与它相同的资源，它就不应该。

** 注意：事实上，我不是关于std::string获取任何资源，而是关于获取任何资源。

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