类的大小限制是多少？ [英] What is the size limit for a class?

问题描述

我想知道一个类的大小限制是什么。我做了一个简单的测试：

I was wondering what the size limit for a class is. I did a simple test:

#define CLS(name,other) \
class name\
{\
public: \
name() {};\
   other a;\
   other b;\
   other c;\
   other d;\
   other e;\
   other f;\
   other g;\
   other h;\
   other i;\
   other j;\
   other k;\
};

class A{
   int k;
public:
   A(){};
};

CLS(B,A);
CLS(C,B);
CLS(D,C);
CLS(E,D);
CLS(F,E);
CLS(G,F);
CLS(H,G);
CLS(I,H);
CLS(J,I);

无法编译

'J'：类太大

"'J' : class is too large"

如果我删除最后声明 - <$ c $

If I remove the final declaration - CLS(J,I);, it all compiles fine.

这是一个编译器强加的限制，或者它在某处标准？

Is this a compiler-imposed restriction, or is it somewhere in the standard?

推荐答案

在C ++ 11中这是附件B.实现可以施加限制，但是它们应该至少：

In C++11 this is Annex B. Implementations can impose limits, but they should be at least:

• 对象的大小[262 144]。


• 单个类中的数据成员[16 384]。


• 在单个类中声明的成员[4 096]。

一个不直接与你使用的结构类型，我提到它只是因为它表明第二个是确实是总成员，可能包括那些在基地，我不是确定关于成员的成员。

The third one isn't directly relevant to the kind of construction you're using, I mention it just because it indicates that the second one is indeed the total members, presumably including those in bases and I'm not sure about members-of-members. But it's not just about the members listed in a single class definition.

您的实现似乎已经放弃了2 ^ 31个数据成员，或者大小为2 ^ 32，因为它接受 I ，但不接受 J 。显然，编译器拒绝考虑大于 SIZE_MAX 的类，即使程序没有实例化或使用 sizeof 上的类型。因此，即使在编译器方面尽最大努力，我也不会期望在32位实现上工作。

Your implementation appears to have given up either 2^31 data members, or at size 2^32, since it accepts I but not J. It's fairly obviously reasonable for a compiler to refuse to consider classes with size greater than SIZE_MAX, even if the program happens not to instantiate it or use sizeof on the type. So even with the best possible effort on the part of the compiler I wouldn't ever expect this to work on a 32 bit implementation.

请注意，这些数量只有准则和不确定遵从，因此即使在具有足够的资源来编译使用更大数目的程序的情况下，一致的含义也可以施加任意更小的限制。

Note that "these quantities are only guidelines and do not determine compliance", so a conforming implication can impose an arbitrary smaller limit even where it has sufficient resources to compile a program that uses larger numbers. There's no minimum limit for conformance.

C ++标准中有各种机会，因为合理的实现由于可笑的小资源限制而无用，所以没有额外的危害如果这是另一个。

There are various opportunities in the C++ standard for a conforming implementation to be useless due to ridiculously small resource limits, so there's no additional harm done if this is another one.

C ++ 03是大致相同的：

C++03 is more-or-less the same:

• 对象的大小[262 144]。


• 单个类，结构或联合中的数据成员[16 384]。


• 在单个类中声明的成员[4 096]。

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