blocks|key|1078638|text|我知道两个原因：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1078639|无符号整数别名，在不同的体系结构中，一个类型可以是不同的声明，就像非常简单的例子:+u32，在某些地方可以被定义为|1078640|，其他无符号的simpler|unordered-list-item|1078641|Portability，类型。|1078642|1078643|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|O|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

I know two reasons:

<ul>
<li>Aliasing, turning complex declaration something simpler</li>
<li>Portability, at different architecture, a type could be differently just, as very simple example: u32, where at some places could be defined as unsigned int, other unsigned long type.</li>
</ul>

blocks|key|1078692|text|我看到人们这样做的原因之一是，他们认为，如果需要更改实际类型，他们只需更改typedef。不过，我对这一论点并不太信服。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1078693|entityMap^0|11|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

One of the reason I have seen people do this is that they think the if there is a need to change the actual type they just have to change the <code>typedef</code>. I am not too convined about that argument though.

blocks|key|1078920|text|类型定义的目的之一是可移植性。例如，不同的编译器和平台有不同的类型大小，例如x86，Linux上的sizeof(+int+)，gcc与德州仪器的处理器上的sizeof(Int)不同:)但它仍然是int。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1078921|所以,|1078922|typedef+int+INT32+|code-block|syntax|javascript|1078923|在移植代码时保存一个。|1078924|typedef的另一个目的是声明类型，以便进行更短的声明。|1078925|typedef+sharted_ptr<MyClass>+MyClassPtr;|1078926|现在，您可以使用MyClassPtr作为类型，而不是编写整个shared_ptr...字符串。|offset|length|style|CODE|1078927|以及带有结构的typedef的非常常见的用法：|1078928|typedef+struct+{
+++int+x;
+++int+y;
}+Point;|1078929|或|1078930|struct+point+{
+++int+x;
+++int+y;
}

typedef+struct+point+Point;|1078931|这两种类型定义都可以避免每次都键入struct关键字。|1078932|entityMap^0|0|0|0|0|0|0|8|A|0|0|0|0|0|H|6|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|1B|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|1C|8|@$Q|1D|R|1E|S|T]]|9|@]|A|$]]|$1|U|3|V|5|6|7|1F|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|11|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|12|3|13|5|6|7|1J|8|@$Q|1K|R|1L|S|T]]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]]|15|$]]

One of the typedef purposes is portability. E.g. different compilers and platforms have various type sizes, e.g. sizeof(int) on x86, Linux, gcc is not the same as on Texas Instrument's processors :) But it's still int. 

So, 

<pre><code>typedef int INT32 
</code></pre>

saves one when porting the code. 

Another purpose of typedef, is to declare types in order to make shorter declarations. 

<pre><code>typedef sharted_ptr&lt;MyClass&gt; MyClassPtr;
</code></pre>

And now, you can use <code>MyClassPtr</code> as a type, instead of writing the whole shared_ptr... string.

And the very common usage of typedef with structures:

<pre><code>typedef struct {
 int x;
 int y;
} Point;
</code></pre>

or 

<pre><code>struct point {
 int x;
 int y;
}

typedef struct point Point;
</code></pre>

Both typedefs let you avoid typing <code>struct</code> keyword every time.

blocks|key|1141396|text|这样做通常是为了代码的可移植性，并且与嵌入式系统特别相关。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1141397|假设你有一些整数值，绝对必须是32位的长度。也许他们需要映射到网络/磁盘结构，也许他们需要保持这么大的值，或者其他什么。|1141398|现在，假设你在一个'int‘是32位的编译器上开发你的代码。你写..。|1141399|struct+s+{
+int+a,b,c,d;
}|code-block|syntax|javascript|1141400|...and它工作得很好。但是，如果需要切换到int仅为16位，而long为32位的编译器，则需要将所有这些声明更改为|1141401|struct+s+{
+long+a,b,c,d;
}|1141402|更糟糕的是，你不能只做搜索/替换，因为一些“int”你可能不关心它的大小。因此，最好的方法是：|1141403|typedef+long+INT32;+//+change+this+typedef+according+to+compiler

struct+s+{
+INT32+a,b,c,d;
}|1141404|然后，您所需要做的就是更改typedefs。|1141405|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|11|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|H|7|13|8|@]|9|@]|A|$I|J]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

It's often done for code portability, and is particularly relevant for embedded systems.

Suppose you have some integer values that absolutlely MUST be 32-bits long. Maybe they need to map to network/disk structures, maybe they need to hold values of that magnitude, or whatever.

Now, suppose you develop your code on a compiler where 'int' is 32 bits. You write...

<pre><code>struct s {
 int a,b,c,d;
}
</code></pre>

...and it works fine. But, if you need to switch to a compiler where int is only 16-bits, but long is 32, you would need to change all those declarations to

<pre><code>struct s {
 long a,b,c,d;
}
</code></pre>

Worse yet, you can't do just search/replace, because some of the 'ints' you probably don't care about the size. So, the best approach is to to this:

<pre><code>typedef long INT32; // change this typedef according to compiler

struct s {
 INT32 a,b,c,d;
}
</code></pre>

Then, all you need to is change the typedefs.

blocks|key|1078934|text|原因可能是他们希望在移植代码时更改指针类型。在另一个系统上，可能有不同的寻址模式(“be”等)，然后它们可能需要使用非标准语法，如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1078935|typedef+far+intptr_t++++++++ngx_int_t;+|code-block|syntax|javascript|1078936|如果它们从不将代码移植到同一系统上具有多个寻址模式的任何系统，那么指针的可移植性将永远不会成为问题，而typedef将是多余的。|1078937|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

The reason could be that they wish to change the pointer type when porting the code. On another system, there might be different addressing modes ("banking" etc), and then they might need to use non-standard syntax, like

<pre><code>typedef far intptr_t ngx_int_t; 
</code></pre>

If they never port the code to any system with more than one addressing mode on the same system, portability of pointers would never be an issue and the typedef would be redundant.

<pre><code>typedef intptr_t ngx_int_t; 
typedef uintptr_t ngx_uint_t; 
typedef intptr_t ngx_flag_t;
</code></pre>

What can we benifit from this ?I can't think of one to be honest...

The above code are from the famous nginx project,check it if interested.

What's the purpose of these `typedef`?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

typedef intptr_t        ngx_int_t; typedef uintptr_t       ngx_uint_t; typedef intptr_t        ngx_flag_t;我们能从中得到什么好处?老实说，我想不出一个...以上代码来自著名的nginx项目，如果感兴趣，请查看。

问这些“typedef`”的用途是什么？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问这些“typedef`”的用途是什么？EN