blocks|key|1892052|text|在您描述的情况下，gcc会给出一个警告：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1892053|./x.c:3010:+warning:+'someName'+defined+but+not+used|code-block|syntax|javascript|1892054|解决方案:做你当前正在做的事情，但不要忽视编译器警告;)|1892055|编辑：|BOLD|1892056|对于你更新的问题:不，我不相信有一种方法可以简单地声明一个静态变量(而不定义它)。|1892057|常见的解决方案是确保所有的全局作用域变量只声明一次，如果需要，可以使用初始化器。|1892058|entityMap^0|9|3|0|0|0|0|3|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Z|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|10|8|@$9|11|A|12|B|O]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|13|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|14|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|U|$]]

<code>gcc</code> will give a warning in the case you've described:

<pre><code>./x.c:3010: warning: 'someName' defined but not used
</code></pre>

Solution: Do what you're currently doing, but don't ignore compiler warnings ;)

Edit:

With your updated question: No, I don't believe there is a way to simply declare a static variable (without also defining it).

The common solution is just to make sure all your global scope variables are declared once only, with an initialiser if they need it.

blocks|key|1892029|text|static+some_type+some_name;+/*definition+*/|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1892030|静态变量some_name已被初始化为0；它是定义，而不仅仅是声明。|unstyled|1892031|在IMO中，静态变量不能只在C中使用外部说明符声明，因为它的链接总是内部的。|1892032|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>static some_type some_name; /*definition */
</code></pre>

The static variable some_name has been initialized by 0; it is the definition, not just a declaration.

IMO, a static variable cannot be just declared in C using extern specifier as its linkage is always internal.

blocks|key|646585|text|不可能在C语言中创建具有内部链接的对象的非定义声明(也就是您的术语中的“预声明”)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|646586|这是一个暂定的定义，也就是您在示例中的定义。但在打字错误的情况下，暂定的定义将隐含地产生一个独立的定义，而不是链接器错误。|646587|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

It is not possible to create a non-defining declaration (i.e. "pre-declare" in your terminology) of an object with internal linkage in C language. 

As close as you can get to that is a tentative definition, which is what you have in your example. But in case of a typo tentative defintion will implictly produce an independent definition, not a linker error.

blocks|key|2054506|text|下面是一些背景知识：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2054507|正如其他人指出的那样，静态变量具有内部链接，这意味着它们只能在相同的“编译单元”或源文件中使用。这意味着您不能在一个头文件中声明它，在一个编译单元中为它赋值，然后期望该值出现在另一个编译单元中。|2054508|初始化全局变量(静态变量或非静态变量)时，编译器只是将初始值放入分配给该变量的内存位置的可执行文件中。换句话说，它总是有一个初始值。当然，您可以在以后使用赋值语句覆盖该值。|2054509|建议：|2054510|如果您确实不知道编译时变量的值，那么您应该在初始化函数中动态分配它。|2054511|static+some_type+some_variable;+/*+=+0+by+default+*/

/*+some+code+*/

void+MyInitializations()
{
++++some_variable+=+some_value;
}|code-block|syntax|javascript|2054512|如果你想在一个地方声明变量，比方说一个头文件，并在一个源文件中定义它，那么你应该使用一个'extern‘声明，它告诉编译器不要担心变量在哪里。链接器将找到变量的位置，就像它在另一个文件中找到函数并填充地址一样。|2054513|标题：|2054514|extern+some_type+some_variable;|2054515|源文件1：|2054516|void+UseSomeVariable()
{
++++x+=+some_variable;
}|2054517|源文件2：|2054518|some_type+some_variable+=+some_value;

/*+possible+also+uses+some_variable+*/|2054519|如果你只想在一个地方声明变量，在另一个地方定义它，不要使用'static‘关键字。这样做的缺点是不能在不同的编译单元(.c文件)中使用相同的全局变量，也不能在头文件中使用它。|2054520|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|18|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|19|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1A|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1B|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1C|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|T|5|L|7|1E|8|@]|9|@]|A|$M|N]]|$1|U|3|V|5|6|7|1F|8|@]|9|@]|A|$]]|$1|W|3|X|5|L|7|1G|8|@]|9|@]|A|$M|N]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|11|5|L|7|1I|8|@]|9|@]|A|$M|N]]|$1|12|3|13|5|6|7|1J|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1K|8|@]|9|@]|A|$]]]|15|$]]

A little background:

As others have pointed out, static variables are have internal linkage, which means that they can only be used in the same "compilation unit" or source file. That means you cannot declare it in a header file, assign a value to it in one compilation unit, and expect that value to appear in another.

When you initialize a global variable (static or not), the compiler simply puts the initial value into the executable file at the memory location allocated for the variable. In other words, it always has an initial value. Of course you can always override the value later by using an assignment statement.

Suggestions:

If you really don't know the value of the variable at compile-time, then you should assign it dynamically in your initialization function.

<pre><code>static some_type some_variable; /* = 0 by default */

/* some code */

void MyInitializations()
{
 some_variable = some_value;
}
</code></pre>

If you want to declare the variable in one place, say a header file, and define it in a source file, then you should use an 'extern' declaration which tells the compiler to not worry about where the variable is. The linker will find the location of the variable much like it finds a function in another file and fill in the address.

Header:

<pre><code>extern some_type some_variable;
</code></pre>

Source file 1:

<pre><code>void UseSomeVariable()
{
 x = some_variable;
}
</code></pre>

Source file 2:

<pre><code>some_type some_variable = some_value;

/* possible also uses some_variable */
</code></pre>

If you just want to declare the variable in one place and define it in another, don't use the 'static' keyword. The downside of this is that you can't use the same global variable in different compilation units (.c files) and you can't use it in a header file.

blocks|key|1889982|text|你需要预先声明变量吗？如果不是，则将初始化器放在唯一的声明上。如果你的初始化器不是一个常量(这需要C%2B%2B，而不是C，IIRC)，那么我可以理解为什么你需要在一些使用它的函数之前预先声明它。但是，初始化程序所需的所有内容都可以在初始化程序之前预先声明。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1889983|因此，将常量defs和静态变量放在每个文件的顶部，这样静态变量的初始化器就可以紧跟在常量之后。这样你就不需要单独的初始化行了。|1889984|在任何其他情况下，caf都是正确的:为了从它的警告中获益，让你的代码和gcc一起编译是值得的。我已经为C%2B%2B中的MFC+GUI的g%2B%2B做到了这一点。(编译而不是运行！)|1889985|AFAIK+C没有办法编写一个弱定义，如果以后没有带有初始化器的定义，就会产生错误。因为变量放在BSS部分，所以总是有一个隐式的0。|1889986|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Do you need to pre-declare the variable? If not, then put the initializer on the only declaration. If your initializer is not a constant (which would require C++, not C, IIRC), then I can understand why you need to pre-declare it before some functions that use it. But then everything you need for the initializer could be pre-declared before it.

So put your constant defs and static variables up at the top of each file, so your initializer for the static can come right after the constants. Then you don't need a separate initialization line.

In any other case, caf's right: It can be worth getting your code to compile with gcc just to get the benefit of its warnings. I've done that for g++ for an MFC GUI in C++. (compile, not run!)

AFAIK C doesn't have a way to write a weak definition that will produce an error if there isn't a definition with an initializer later. There's always an implicit 0, since the variable goes in the BSS section.

blocks|key|2054449|text|如果我理解你的问题，也许你只是没有以正确的方式面对它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2054450|你能不能更好地使用extern+SomeType+someVar_;，它对你的程序说，我知道这个变量是已知的，但我不想告诉你现在它是什么。|offset|length|style|CODE|2054451|因此，您可以在一个单独的文件中声明您的变量|2054452|static+SomeType+SomeVar_;|2054453|在您的文件中，将|2054454|extern+SomeType+SomeVar_|2054455|然后把初始化放在你想要的任何地方。|2054456|entityMap^0|0|9|P|0|0|0|P|0|0|0|O|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@$D|V|E|W|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|X|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Y|8|@$D|Z|E|10|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|11|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|12|8|@$D|13|E|14|F|G]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|15|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|S|$]]

If I understand your problem maybe your just not facing it the right way.

Would you not be better with <code>extern SomeType someVar_;</code> which says to your program, I know that this variable will be known, but I don't want to tell you what it is now.

You can therefore, in a separate file declare your variable say

<code>static SomeType SomeVar_;</code>

In your file, put

<code>extern SomeType SomeVar_</code>

And than put the initialization wherever you want.

Some times we need to pre-declare a static variable and then use it.
But the variable name of this declaration may be wrong, and the compiler can not detect it, oops!

Example:

<pre><code>/* lots of codes */
static some_type some_name; /* pre-declaration */
 /* but it may define "some_name" */
/* use some_name */

/* lots of codes */

static some_type someName = initialization; /* definition */
/* use someName */

/* lots of codes */
</code></pre>

"some_name" and "someName" are different, we use a wrong variable at the begin.
If the pre-declaration statement does not define any thing, the compiler will detect the mistake.

So, how to declare a static variable but not define it? How can I change the pre-declaration to a new one which makes compiler can detects wrong names?

How to declare a static variable but not define it

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。

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有时我们需要预先声明一个静态变量，然后再使用它。但是这个声明的变量名可能是错误的，编译器无法检测到它，哦！示例：/* lots of codes */static some_type some_name; /* pre-declaration */                            /* but it may define "some_name" *//* use some_n

问如何声明静态变量但不定义它
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