typedef结构体对自身的影响是什么？ [英] What is the effect of typedef'ing a struct to itself?

问题描述

我看到这个代码写在一个API的顶部：

I've seen this code written at the top of an API:

typedef struct SYSTEM SYSTEM;

类型 SYSTEM 以前未定义。有谁知道这是什么？编译器认为 SYSTEM 之后是什么？

The type SYSTEM was previously undefined. Does anyone know what this does? What does the compiler think a SYSTEM after this line?

感谢您的答案！我的问题是SYSTEM之前没有在文件中定义，所以我不知道它是什么。例如，该行将自行编译，但 struct SYSTEM 未在任何位置定义。

Thanks for the answers! My question is that SYSTEM was not previously defined in the file, so I have no idea what it is. For example, that line will compile by itself, but struct SYSTEM was not defined anywhere.

推荐答案

它允许你在C中使用名称 SYSTEM ，而不是使用 struct SYSTEM 。
typedef 创建一个同义词 SYSTEM 到 struct SYSTEM 。

It allows you in C to use the name SYSTEM instead of using struct SYSTEM. The typedef creates a synonym SYSTEM to struct SYSTEM.

在 struct SYSTEM 未声明的情况下，声明还声明 struct SYSTEM 作为一个不完整的类型，如下面的声明： struct SYSTEM; 。

In your case as struct SYSTEM is not declared, the declaration also declares struct SYSTEM as an incomplete type like in this declaration: struct SYSTEM;.

然后可以在另一个翻译单元中声明完整的对象类型 struct SYSTEM 。

The complete object type struct SYSTEM can then be declared in another translation unit.

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