什么是'结构点¯xtypedef`主场迎战`typedef结构X`的意义？ [英] What is the meaning of `struct X typedef` vs. `typedef struct X`?

问题描述

我必须在现有code碱基以下（工作）code，应用于包括C和C ++之间共享文件，编译于MSVC（2010）和Windows DDK：

I have the following (working) code in an existing code base, used in include file that is shared between C and C++, compiling on MSVC (2010) and Windows DDK:

struct X {
    USHORT x;
} typedef X, *PX;

和

enum MY_ENUM {
    enum_item_1,
    enum_item_2 
} typedef MY_ENUM;

据我所知，正确的定义应该是这样的：

As far as I know, correct definition should look like this:

typedef struct {
    USHORT x;
} X, *PX;

有什么目的，其具有以下形式？我缺少的东西吗？

Is there any purpose for having the form below? Am I missing something?

推荐答案

事实上，这两个的typedef＆LT;＆型GT; ＆LT;＆别名GT; 和＆LT;＆型GT;的typedef＆LT;别名方式＆gt; 有效期只是来自于语言的语法定义

The fact that both typedef <type> <alias> and <type> typedef <alias> are valid simply comes from the language grammar definition.

的typedef 被列为存储类specfifier 的（就像静态， 汽车），并且类型本身是被称为的类型说明符的。从标准的6.7节的语法定义，你会发现这些都是免费进行互换：

typedef is classified as a storage-class specfifier (just like static, auto), and the type itself is known as the type-specifier. From the syntax definitions in section 6.7 of the standard, you'll see that these are free to be interchanged:

declaration:
    declaration-specifiers init-declarator-list ;

declaration-specifiers:
    storage-class-specifier declaration-specifiers
    type-specifier declaration-specifiers
    type-qualifier declaration-specifiers
    function-specifier declaration-specifiers

init-declarator-list:
    init-declarator
    init-declarator-list , init-declarator

init-declarator:
    declarator
    declarator = initializer

（注意，当然，这也同样如此结构和非结构的，这意味着双typedef的麻烦; 也是有效的）

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