为什么当我添加实例到一个向量时，我的类的析构函数被调用？ [英] Why does my class's destructor get called when I add instances to a vector?

问题描述

看来每次向向量m_test添加一个对象时，都会调用destructor方法。我缺少什么？如何防止这种情况的发生？

It seems that every time I add an object to the vector m_test, the destructor method is called. Am I missing something? How can I prevent this from happening?

class TEST
{
public:
    TEST();
    ~TEST();
    int * x;
};

TEST::TEST()
{
}

TEST::~TEST()
{
... it is called every time I push_back something to the vector ...
    delete x;
}

    vector<TEST> m_test;
    for (unsigned int i=0; i<5; i++)
    {
        m_test.push_back(TEST());
    }

推荐答案

违反了三项规则。你的类有一个析构函数，所以你需要一个复制构造函数和赋值运算符。或者，您不能允许复制您的类（例如通过使 T（T const&）和 T& operator = ） private，或者通过派生 boost :: noncopyable ），然后重新调整向量，而不是使用 push_back 。

The problem here is that you're violating the Rule of Three. Your class has a destructor so you need a copy-constructor and an assignment operator, too. Alternatively, you could not allow your class to be copied (for example by making T(T const&) and T& operator=(T const&) private, or by deriving from boost::noncopyable), and then resize the vector instead of using push_back.

在第一种情况下，你可以像平常一样只需 push_back 第二，语法将像

In the first case, you can just push_back your class as you usually would. In the second, the syntax would be something like

std::vector<TEST> vec(5);
// vec now has five default-constructed elements of type TEST.

没有做这些事情是一个坏主意，因为你很可能会遇到双删除即使你认为你永远不会复制或分配 TEST 其中 x！= nullptr ，它显然禁止它是更安全的。

Not doing either of these things is a bad idea, as you are very likely to run into double deletion issues at some point -- even if you think you'll never copy or assign a TEST where x != nullptr, it's much safer to explicitly forbid it.

顺便说一下，如果你有成员指针，当一个对象超出范围应该删除，请考虑使用智能指针 scoped_ptr ， unique_ptr 和 shared_ptr $ c> auto_ptr 如果您无法使用Boost或C ++ 11）。

By the way, if you have member pointers that should be deleted when an object goes out of scope, consider using smart pointers like scoped_ptr, unique_ptr and shared_ptr (and maybe auto_ptr if you're unable to use Boost or C++11).

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