什么是用C空结构的大小？ [英] What is the size of an empty struct in C?

问题描述

据我来说，这是零，但似乎有一点混乱<一个href=\"http://stackoverflow.com/questions/1626017/why-sizeofspinlockt-is-greater-than-zero-on-uni-processor/1626054#1626054\">here

According to me, it is zero but there seems to be bit confusion here

我与gcc编译器测试，它给了我零输出。我知道，在C ++中，空类的大小为1。让我知道如果我在这里缺少什么。

I have tested it with gcc compiler and it gives me zero as output. I know that in C++, size of an empty class is 1. Let me know if I am missing anything here.

推荐答案

因为语法禁止它结构不能在C空。此外，还有一种语义约束，使得不确定的行为，如果一个结构没有命名的成员：

A struct cannot be empty in C because the syntax forbids it. Furthermore, there is a semantic constraint that makes behavior undefined if a struct has no named member:

struct-or-union-specifier:
  struct-or-union identifieropt { struct-declaration-list }
  struct-or-union identifier

struct-or-union:
  struct
  union

struct-declaration-list:
  struct-declaration
  struct-declaration-list struct-declaration

struct-declaration:
  specifier-qualifier-list struct-declarator-list ;

/* type-specifier or qualifier required here! */
specifier-qualifier-list:
  type-specifier specifier-qualifier-listopt
  type-qualifier specifier-qualifier-listopt

struct-declarator-list:
  struct-declarator
  struct-declarator-list , struct-declarator

struct-declarator:
  declarator
  declaratoropt : constant-expression

如果你写

struct identifier { };

这会给你一个诊断信息，因为你违反语法规则。如果你写

It will give you a diagnostic message, because you violate syntactic rules. If you write

struct identifier { int : 0; };

那么你有没有命名的成员非空的结构，从而使行为的定义，而不是要求一个诊断：

Then you have a non-empty struct with no named members, thus making behavior undefined, and not requiring a diagnostic:

如果在结构声明列表中没有名称的成员，其行为定义理解过程网络。

If the struct-declaration-list contains no named members, the behavior is undefined.

请注意，以下是不允许的，因为灵活的阵列成员不能成为第一个成员：

Notice that the following is disallowed because a flexible array member cannot be the first member:

struct identifier { type ident[]; };

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