是STL向量调用未分配对象的析构函数吗？ [英] Is STL Vector calling a destructor of a not-allocated object?

问题描述

下面的代码显示了不期望的输出：

The folowing code shows an output not expected:

class test
{
    public:
    test()
    {
        std::cout << "Created" << (long)this << std::endl;
    }
    ~test()
    {
        std::cout << "Destroyed" << (long)this << std::endl;
    }
};

int main(int argc, char** argv)
{
    std::vector<test> v;
    test t;
    v.push_back(t);

    return EXIT_SUCCESS;
}

执行时显示：

Created-1077942161
Destroyed-1077942161
Destroyed674242816

我认为第二个Destroyed输出不应该存在。当我不使用向量时，结果是一个Created和一个Destroyed线如预期。

I think the second "Destroyed" output should not be there. When I don't use the vector the result is one Created and one Destroyed line as expected. Is this behavior normal?

（这是在FreeBSD系统上用GCC编译的）

(This is compiled with GCC on a FreeBSD system)

推荐答案

一切都是应该的：有一个局部变量 t ，它被创建，然后在 main ），并且有 v [0] ，它在 main（）结尾创建和销毁。

Everything is as it should be: there's the local variable t, which gets created and then destroyed at the end of main(), and there's v[0], which gets created and destroyed at the end of main().

您没有看到创建 v [0] 或移动构造函数，您的测试类不提供。 （因此，编译器为您提供了一个，但没有输出。）

You don't see the creation of v[0] because that happens by copy or move constructor, which your test class doesn't provide. (So the compiler provides one for you, but without output.)

为了测试的目的，并且对于所有包含所有可能的构造函数，析构函数，赋值和交换运算符的测试类，并在每个中打印一个诊断线，因此您可以看到对象在容器和算法中使用时的行为。

For testing purposes it's handy to write for yourself once and for all a test class that contains all the possible constructors, destructors, assignment and swap operators and prints a diagnostic line in each, so you can witness how objects behave when used in containers and algorithms.

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