blocks|key|1841480|text|您可以将所有调试调用放在一个函数中，让它称为printf_debug，并将DEBUG放入此函数中。编译器将优化empty函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1841481|entityMap^0|M|C|11|5|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

You can put all your debug call in a function, let call it <code>printf_debug</code> and put the <code>DEBUG</code> inside this function.
The compiler will optimize the empty function.

blocks|key|1953036|text|不，你不能。在预处理指令的任何处理开始之前，注释都会从代码中删除。因此，您不能在宏中包含注释。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1953037|此外，任何试图在以后使用任何宏技巧来“形成”注释的尝试都不能保证有效。编译器不需要将"late“注释识别为注释。|1953038|实现所需功能的最佳方法是在C99中使用带有变量参数的宏(或者，也可以使用编译器扩展)。|1953039|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

No, you can't. Comments are removed from the code before any processing of preprocessing directives begin. For this reason you can't include comment into a macro. 

Also, any attempts to "form" a comment later by using any macro trickery are not guaranteed to work. The compiler is not required to recognize "late" comments as comments.

The best way to implement what you want is to use macros with variable arguments in C99 (or, maybe, using the compiler extensions).

blocks|key|1841528|text|标准方法是使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1841529|#ifndef+DEBUG
++++#define+printd(fmt,+...)++do+{+}+while(0)
#else
++++#define+printd(fmt,+...)+printf(fmt,+__VA_ARGS__)
#endif|code-block|syntax|javascript|1841530|这样，当您在末尾添加分号时，它会执行您想要的操作。由于没有任何操作，编译器将编译出"do...while“|1841531|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 standard way is to use 

<pre><code>#ifndef DEBUG
 #define printd(fmt, ...) do { } while(0)
#else
 #define printd(fmt, ...) printf(fmt, __VA_ARGS__)
#endif
</code></pre>

That way, when you add a semi-colon on the end, it does what you want.
As there is no operation the compiler will compile out the "do...while"

blocks|key|545619|text|С99方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|545620|#ifdef+DEBUG
++++#define+printd(...)+printf(__VA_ARGS__)
#else
++++#define+printd(...)
#endif|code-block|syntax|javascript|545621|好吧，这个不需要C99，但假设编译器已经为发布版本打开了优化：|545622|#ifdef+DEBUG
++++#define+printd+printf
#else
++++#define+printd+if+(1)+{}+else+printf
#endif|545623|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

С99 way:

<pre><code>#ifdef DEBUG
 #define printd(...) printf(__VA_ARGS__)
#else
 #define printd(...)
#endif
</code></pre>

Well, this one doesn't require C99 but assumes compiler has optimization turned on for release version:

<pre><code>#ifdef DEBUG
 #define printd printf
#else
 #define printd if (1) {} else printf
#endif
</code></pre>

blocks|key|539499|text|正如McKay所指出的，如果您简单地尝试用//替换printd，您将会遇到问题。相反，您可以使用可变宏将printd替换为一个不执行任何操作的函数，如下所示。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|539500|#ifndef+DEBUG
++++#define+printd(...)+do_nothing()
#else
++++#define+printd(...)+printf(__VA_ARGS__)
#endif

void+do_nothing()+{+;+}|code-block|syntax|javascript|539501|使用像GDB这样的调试器可能也会有所帮助，但有时一个快速的printf就足够了。|539502|entityMap^0|L|2|P|6|1G|6|0|0|T|6|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

As noted by McKay, you will run into problems if you simply try to replace <code>printd</code> with <code>//</code>. Instead, you could use variadric macros to replace <code>printd</code> with a function that does nothing as in the following.

<pre><code>#ifndef DEBUG
 #define printd(...) do_nothing()
#else
 #define printd(...) printf(__VA_ARGS__)
#endif

void do_nothing() { ; }
</code></pre>

Using a debugger like GDB might help too, but sometimes a quick <code>printf</code> is enough.

blocks|key|1953151|text|一个常见的技巧是这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1953152|#ifdef+DEBUG
++#define+OUTPUT(x)+printf+x
#else
++#define+OUTPUT(x)
#endif

#include+<stdio.h>
int+main(void)
{+++
++OUTPUT(("%25s+line+%25i\n",+__FILE__,+__LINE__));

++return+0;
}|code-block|syntax|javascript|1953153|通过这种方式，您可以使用printf()的全部功能，但您必须忍受双括号才能使宏工作。|offset|length|style|CODE|1953154|双括号的要点是:您需要一个集合来指示这是一个宏调用，但在C89中，宏中不能有不确定数量的参数。但是，通过将参数放在它们自己的一组括号中，它们会被解释为单个参数。在定义DEBUG的情况下展开宏时，替换文本是单词printf后跟singl参数，该参数实际上是括号中的几个项目。然后，这些括号被解释为printf函数调用中所需的括号，因此一切都解决了。|1953155|entityMap^0|0|0|C|8|0|2B|5|2W|6|43|6|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@$I|W|J|X|K|L]|$I|Y|J|Z|K|L]|$I|10|J|11|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|P|$]]

A common trick is to do this:

<pre><code>#ifdef DEBUG
 #define OUTPUT(x) printf x
#else
 #define OUTPUT(x)
#endif

#include &lt;stdio.h&gt;
int main(void)
{ 
 OUTPUT(("%s line %i\n", __FILE__, __LINE__));

 return 0;
}
</code></pre>

This way you have the whole power of <code>printf()</code> available to you, but you have to put up with the double brackets to make the macro work.

The point of the double brackets is this: you need one set to indicate that it's a macro call, but you can't have an indeterminate number of arguments in a macro in C89. However, by putting the arguments in their own set of brackets they get interpreted as a single argument. When the macro is expanded when <code>DEBUG</code> is defined, the replacement text is the word <code>printf</code> followed by the singl argument, which is actually several items in brackets. The brackets then get interpreted as the brackets needed in the <code>printf</code> function call, so it all works out.

blocks|key|545737|text|我经常使用这个结构：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|545738|#define+DEBUG+1
#if+DEBUG
#if+PROG1
#define+DEBUGSTR(msg...)++++++++{+printf("P1:+");+printf(+msg);+}
#else
#define+DEBUGSTR(msg...)++++++++{+printf("P2:+");+printf(+msg);+}
#endif
#else
#define+DEBUGSTR(msg...)++++((void)+0)
#endif|code-block|syntax|javascript|545739|这样我就可以在我的控制台上知道哪个程序给出了哪个错误消息……此外，我可以很容易地搜索我的错误消息...|545740|就我个人而言，我不喜欢#只定义表达式的一部分...|545741|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I use this construct a lot:

<pre><code>#define DEBUG 1
#if DEBUG
#if PROG1
#define DEBUGSTR(msg...) { printf("P1: "); printf( msg); }
#else
#define DEBUGSTR(msg...) { printf("P2: "); printf( msg); }
#endif
#else
#define DEBUGSTR(msg...) ((void) 0)
#endif
</code></pre>

This way I can tell in my console which program is giving which error message... also, I can search easily for my error messages... 

Personally, I don't like #defining just part of an expression...

blocks|key|545784|text|它已经完成了。我不推荐这样做。没有时间测试，但机制是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|545785|+#define+printd_CAT(x)+x+##+x
+#ifndef+DEBUG
++++#define+printd+printd_CAT(/)
+#else
++++#define+printd+printf
+#endif|code-block|syntax|javascript|545786|如果您的编译器在编译器本身中处理//注释，这将起作用(不能像ANSI保证/*注释有两次传递)。|545787|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|$]]

It's been done. I don't recommend it. No time to test but the mechanism is kind of like this:

<pre><code> #define printd_CAT(x) x ## x
 #ifndef DEBUG
 #define printd printd_CAT(/)
 #else
 #define printd printf
 #endif
</code></pre>

This works if your compiler processes // comments in the compiler itself (there's no guarantee like the ANSI guarantee that there are two passes for /* comments).

blocks|key|1839234|text|未测试:编辑:已测试，现在由我自己使用:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1839235|#define+DEBUG+1
#define+printd(fmt,...)+if(DEBUG)printf(fmt,+__VA_ARGS__)|code-block|syntax|javascript|1839236|要求您不仅要定义DEBUG，还要给它一个非零值。|offset|length|style|CODE|1839237|附录:也可以很好地与std::cout配合使用|1839238|entityMap^0|0|0|8|5|0|A|9|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@$I|W|J|X|K|L]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Untested:
Edit: Tested, using it by myself by now :)

<pre><code>#define DEBUG 1
#define printd(fmt,...) if(DEBUG)printf(fmt, __VA_ARGS__)
</code></pre>

requires you to not only define <code>DEBUG</code> but also give it a non-zer0 value.

Appendix:
Also works well with <code>std::cout</code>

blocks|key|1953303|text|在某些编译器(包括MS+VS2010)上，这将起作用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1953304|#define+CMT+/+##+/|code-block|syntax|javascript|1953305|但是没有所有编译器的被授权者。|1953306|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|$]]

On some compilers (including MS VS2010) this will work,

<pre><code>#define CMT / ## /
</code></pre>

but no grantees for all compilers.

blocks|key|545830|text|在C%2B%2B17中，我喜欢使用constexpr来做这样的事情|type|unstyled|depth|inlineStyleRanges|entityRanges|data|545831|#ifndef+NDEBUG
constexpr+bool+DEBUG+=+true;
#else
constexpr+bool+DEBUG+=+false;
#endif|code-block|syntax|javascript|545832|然后你可以这样做|545833|if+constexpr+(DEBUG)+/*+debug+code+*/|545834|需要注意的是，与预处理器宏不同，您的作用域是有限的。既不能在一个调试条件中声明可从另一个调试条件访问的变量，也不能在外部函数范围中使用它们。|545835|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

In C++17 I like to use constexpr for something like this

<pre><code>#ifndef NDEBUG
constexpr bool DEBUG = true;
#else
constexpr bool DEBUG = false;
#endif
</code></pre>

Then you can do

<pre><code>if constexpr (DEBUG) /* debug code */
</code></pre>

The caveats are that, unlike a preprocessor macro, you are limited in scope. You can neither declare variables in one debug conditional that are accessible from another, nor can they be used at outside function scopes.

blocks|key|545858|text|您可以利用if。例如,|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|545859|#ifdef+debug
++++#define+printd+printf
#else+
++++#define+printd+if+(false)+printf
#endif|code-block|syntax|javascript|545860|如果你设置了像-O2这样的优化标志，编译器将删除这些不可达的代码。此方法对std::cout也很有用。|545861|entityMap^0|5|2|0|0|7|3|11|9|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

You can take advantage of <code>if</code>. For example, 

<pre><code>#ifdef debug
 #define printd printf
#else 
 #define printd if (false) printf
#endif
</code></pre>

Compiler will remove these unreachable code if you set a optimization flag like <code>-O2</code>. This method also useful for <code>std::cout</code>.

I'm trying to do a debug system but it seems not to work.

What I wanted to accomplish is something like this:

<pre><code>#ifndef DEBUG
 #define printd //
#else
 #define printd printf
#endif
</code></pre>

Is there a way to do that? I have lots of debug messages and I won't like to do:

<pre><code>if (DEBUG)
 printf(...)

code

if (DEBUG)
 printf(...)

...
</code></pre>

Can you #define a comment in C?

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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我试图做一个调试系统，但它似乎不工作。我想要实现的东西是这样的：#ifndef DEBUG    #define printd //#else    #define printd printf#endif有没有办法做到这一点？我有很多调试消息，我不喜欢这样做：if (DEBUG)    printf(...)codei...

问你能用C #定义一个注释吗？
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问你能用C #定义一个注释吗？EN