如何看待VS與cpluscplus com中is pod示例的不同輸出？

1樓：藍色

Visual Studio 2013 這裡是 C++98/03的體現，所以實現的不太好，畢竟應該是C++11了。

POD(Plain Old Data)在C++98/03標準中，其實是到處「散落」的，但是針對你的Case來說。首先根據C++03標準的9.4節來說，是這樣的：

A POD-struct is anaggregate classthat hasno non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-defined copy assignment operatorand no user-defined destructor.Similarly, a POD-union is an aggregate union that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-defined copy assignment operator and no user-defined destructor. A POD class is a class that is either a

POD-struct or a POD-union.non-static data members of type non-POD struct, non-POD union (or array of such types). Similarly, a POD union is a union that is both a trivial class and a standard-layout class, and has no non-static data members of type non-POD struct, non-POD union (or array of such types).

A POD classis a class that iseither a POD struct or a POD union.

這裡和C++03相比也不再是說是aggregate class，而是強調更具體的trival class和standard-layout class.

而對於trival class來說，標準在第9章第6條也定義了

A trivial class is a class thathas a default constructor(12.1), has no non-trivial default constructors, and is trivially copyable

A trivially copyable class is a class that:

— has no non-trivial copy constructors (12.8),

— has no non-trivial move constructors (12.8),

— has no non-trivial copy assignment operators (13.5.3, 12.8),

— has no non-trivial move assignment operators (13.5.3, 12.8), and

— has a trivial destructor (12.4).

而standard-layout在第9章第7條為

A standard-layout class is a class that:

— has no non-static data members of type non-standard-layout class (or array of such types) or reference,

— has no virtual functions (10.3) and no virtual base classes (10.1),

— has the same access control (Clause 11) for all non-static data members,

— has no non-standard-layout base classes,

— either has no non-static data members in the most derived class and at most one base class with

non-static data members, or has no base classes with non-static data members, and

— has no base classes of the same type as the first non-static data member

於是只要可以滿足trival和standard-layout的在C++11中就可以是POD

而我之前加粗trivia class has a default constructor. 是想說只要有乙個default constructor，即使我們加上了自定義的constructor也是POD了，引用你的例子稍加改動

structA;

// C-struct (POD)

classB:

publicA};

// still POD

structC:

B};// still POD (member function)

structD:

C};// no POD (custom default constructor)

這裡依然可以得到B是POD的結果，因為B() = default是default constructor的，

然而如果是這樣

structA;

// C-struct (POD)

classB:

publicA};

// not POD

structC:

B};// not POD

structD:

C};// no POD (custom default constructor)

這個時候B就不是POD了，因為B(){}是自定義的constructor了

於是講到這裡，我想也應該懂得C++11的

std::is_trivial

std::is_trivially_copyable

std::is_standard_layout

為什麼叫這些名字了，這些名字也不是隨便取出來的，是有原因的。

如何看待VS與cpluscplus com中is pod示例的不同輸出？

如何看待熊孩子vs暴躁老哥？

如何看待 2016 2017 賽季雷霆VS湖人，尼克楊的絕殺？

如何看待明天鵜鶘vs快船的比賽？

其他用戶還看了：