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Empty class in C++
What is the size of an empty struct in C?

I read somewhere that size of an empty struct in C++ is 1. So I thought of verifying it. Unfortunately I saved it as a C file and used <stdio.h> header and I was surprised to see the output. It was 0.

这意味着:

struct Empty {

};

int main(void)
{
  printf("%d",(int)sizeof(Empty));
}

0 页: 1 汇编成C++文档。我想知道原因。页: 1 C++的空洞结构并非零,因为如果大小为<0>0<>>>/代码>,那么该类的两种物体就会有相同的地址,不可能。我在哪里错了?

Answer 1

You cannot have an empty structure in C. It is a syntactic constraint violation. However gcc permits an empty structure in C as an extension. Furthermore the behaviour is undefined if the structure does not have any named member because

说:

如果“方向声明”清单没有指定成员,行为就没有界定。

So

struct Empty {}; //constraint violation

struct Empty {int :0 ;}; //no named member, the behaviour is undefined.

空洞结构的大小是C++ 。

Answer 2

有几个很好的理由。除其他外,这是为了确保位于该结构的点子上点的点子测量不会导致无限的循环。更多信息:

http://bytes.com/topic/c/insights/660463-sizeof-/2006/3y-1-a

Answer 3

这里是一条可贵的条款,它描述了为什么发生这种情况,更相关的是围绕它采取(安全)的方式:

rel=“noretinger”> http://www.cantrip.org/oneyopt.html。

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