这是struct POD在C ++ 11？ [英] Is this struct POD in C++11?

问题描述

这个结构是C ++ 11中的POD吗？

Is this struct a POD in C++11?

struct B
{
  int a;
  B(int aa) : a(aa) {}
  B() = default;
};

请注意，这个问题是关于 C ++ 11 的。我知道这个类不是C ++ 98和C ++ 03中的POD。

Note that this question is explicit about C++11. I know that this class is not a POD in C++98 nor C++03.

有关C ++ 11中POD的说明，请参阅平凡与标准版面对比POD

For an explanation of POD in C++11, see trivial vs. standard layout vs. POD

（受此问题启发：是否有编译时func /宏来确定C ++ 0x结构是否是POD？）

推荐答案

是的，它是一个POD根据

Yes, it is a POD according to the new rules.

如果你查阅段落8.4.2节/ 4节的新标准，你可以看到如果一个构造函数默认在第一个声明，它不是用户提供：

If you look up paragraph §8.4.2/4 of the new standard, you can see that if a constructor is defaulted on the first declaration, it is not user-provided:

默认函数和隐式声明的函数是
，统称为 defaulted 函数，实现
为它们提供隐式定义（&12; 12; 12.4，&这可能
意味着将它们定义为已删除。如果是用户声明的并且没有明确默认或者在第一个声明中删除
，则特殊成员函数是
用户提供的。 （...）

Explicitly-defaulted functions and implicitly-declared functions are collectively called defaulted functions, and the implementation shall provide implicit definitions for them (§12.1 §12.4, §12.8), which might mean defining them as deleted. A special member function is user-provided if it is user-declared and not explicitly defaulted or deleted on its first declaration. (...)

您可以使用 std :: is_pod 类型trait让编译器用 static_assert 测试此。

You can use the std::is_pod type trait to have the compiler test this for you with static_assert.

static_assert(std::is_pod<B>::value, "B should be a POD");

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