整理：C/C++可变参数，“## __VA_ARGS__”宏的介绍和使用

梦里梦外; 2022-06-09 02:13 330阅读 0赞

今天阅读代码的时候，在一个宏定义语句中，发现了个之前未曾见过的编译器预定义宏：“\_\_VA\_ARGS\_\_”。当时，从代码语句中推测它代表宏参数：“…”（本文称之为省略号），依稀记得printf函数声明中有使用这个省略号，大概的意思是表示可变化的参数，但未深入了解。

在网上看了相关文章的介绍，主要涉及了C/C++函数中可变化参数的基础知识，并延伸到宏定义中的可变参数。借这一次的学习，算是对可变化参数有了比较详细的了解，尤其是解开了一直萦绕在头脑中printf函数声明中这个省略号的疑惑。

为更好了解C/C++中可变参数的知识，我从网上摘录了两篇文章，算是自己的一个总结。本篇主要是关于“\#\# \_\_VA\_ARGS\_\_”宏的介绍和使用。

下文摘自：http://www.cnblogs.com/alexshi/archive/2012/03/09/2388453.html [http://www.cnblogs.com/alexshi/archive/2012/03/09/2388453.html][http_www.cnblogs.com_alexshi_archive_2012_03_09_2388453.html]

在GNU C中，宏可以接受可变数目的参数，就象函数一样，例如:

用可变参数宏(variadic macros)传递可变参数表

你可能很熟悉在函数中使用可变参数表，如:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
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  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">1</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(0,102,153)!important; background:none!important">void</code>&nbsp;<code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(255,20,147)!important; background:none!important">printf</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(0,102,153)!important; background:none!important">const</code>&nbsp;<code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(128,128,128)!important; background:none!important">char</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">* format, ...);</code></td> 
  </tr> 
 </tbody> 
</table>

直到最近，可变参数表还是只能应用在真正的函数中，不能使用在宏中。

C99编译器标准终于改变了这种局面，它允许你可以定义可变参数宏(variadic macros)，这样你就可以使用拥有可以变化的参数表的宏。可变参数宏就像下面这个样子:

缺省号代表一个可以变化的参数表。使用保留名 \_\_VA\_ARGS\_\_ 把参数传递给宏。当宏的调用展开时，实际的参数就传递给 printf()了。例如:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
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  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">1</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">Debug(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"Y = %d\n"</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">, y);</code></td> 
  </tr> 
 </tbody> 
</table>

而处理器会把宏的调用替换成:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
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  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">1</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(255,20,147)!important; background:none!important">printf</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"Y = %d\n"</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">, y);</code></td> 
  </tr> 
 </tbody> 
</table>

因为debug()是一个可变参数宏，你能在每一次调用中传递不同数目的参数:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
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  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">1</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">debug(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"test"</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">);&amp;nbsp;&nbsp;</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:rgb(0,130,0)!important; background:none!important">// 一个参数</code></td> 
  </tr> 
 </tbody> 
</table>

可变参数宏不被ANSI/ISO C++ 所正式支持。因此，你应当检查你的编译器，看它是否支持这项技术。

用GCC和C99的可变参数宏， 更方便地打印调试信息

gcc的预处理提供的可变参数宏定义真是好用:

如此定义之后，代码中就可以用dbgprint了，例如dbgprint(“%s”, \_\_FILE\_\_);

下面是C99的方法:

新的C99规范支持了可变参数的宏  
具体使用如下:

以下内容为程序代码:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">6</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">LOGSTRINGS(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"hello, %d "</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">, 10);</code></td> 
  </tr> 
 </tbody> 
</table>

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">7</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;&nbsp;&nbsp;</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(0,102,153)!important; background:none!important">return</code>&nbsp;<code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">0;</code></td> 
  </tr> 
 </tbody> 
</table>

但现在似乎只有gcc才支持。

可变参数的宏里的’\#\#’操作说明带有可变参数的宏(Macros with a Variable Number of Arguments)  
在1999年版本的ISO C 标准中，宏可以象函数一样，定义时可以带有可变参数。宏的语法和函数的语法类似。下面有个例子:

这里，’…’指可变参数。这类宏在被调用时，它(这里指’…’)被表示成零个或多个符号，包括里面的逗号，一直到到右括弧结束为止。当被调用时，在宏体(macro body)中，那些符号序列集合将代替里面的\_\_VA\_ARGS\_\_标识符。更多的信息可以参考CPP手册。  
GCC始终支持复杂的宏，它使用一种不同的语法从而可以使你可以给可变参数一个名字，如同其它参数一样。例如下面的例子:

这和上面举的那个ISO C定义的宏例子是完全一样的，但是这么写可读性更强并且更容易进行描述。

GNU CPP还有两种更复杂的宏扩展，支持上面两种格式的定义格式。  
在标准C里，你不能省略可变参数，但是你却可以给它传递一个空的参数。例如，下面的宏调用在ISO C里是非法的，因为字符串后面没有逗号:  
debug (“A message”)  
GNU CPP在这种情况下可以让你完全的忽略可变参数。在上面的例子中，编译器仍然会有问题(complain)，因为宏展开后，里面的字符串后面会有个多余的逗号。

为了解决这个问题，CPP使用一个特殊的’\#\#’操作。书写格式为:

这里，如果可变参数被忽略或为空，’\#\#’操作将使预处理器(preprocessor)去除掉它前面的那个逗号。如果你在宏调用时，确实提供了一些可变参数，GNU CPP也会工作正常，它会把这些可变参数放到逗号的后面。象其它的pasted macro参数一样，这些参数不是宏的扩展。

\#\#还可以起到替换作用  
如:

这里将会把IName变成实际数据.

怎样写参数个数可变的宏  
一种流行的技巧是用一个单独的用括弧括起来的的 “参数” 定义和调用宏, 参数在 宏扩展的时候成为类似 printf() 那样的函数的整个参数列表。

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">2</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-weight:bold!important; min-height:auto!important; color:rgb(0,102,153)!important; background:none!important">if</code>&nbsp;<code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">(n != 0) DEBUG((</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"n is %d\n"</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">, n));</code></td> 
  </tr> 
 </tbody> 
</table>

明显的缺陷是调用者必须记住使用一对额外的括弧。

gcc 有一个扩展可以让函数式的宏接受可变个数的参数。 但这不是标准。另一种 可能的解决方案是根据参数个数使用多个宏 (DEBUG1, DEBUG2, 等等), 或者用逗号玩个这样的花招:

<table style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; width:auto!important; border-collapse:collapse!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
 <tbody style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
  <tr style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important"> 
   <td style="margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:3em!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; color:rgb(175,175,175)!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px 0.3em 0px 0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; text-align:right!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:2.7em!important; line-height:1.1em!important; min-height:auto!important; display:block!important; background:none!important">3</code></td> 
   <td style="margin:0px!important; padding:0px 0px 0px 0.5em!important; border-width:0px 0px 0px 3px!important; border-left-style:solid!important; border-left-color:rgb(108,226,108)!important; outline:0px!important; font-size:1em!important; float:none!important; vertical-align:top!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; word-break:break-all!important; background:none!important"> <code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">DEBUG(</code><code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; color:blue!important; background:none!important">"i = %d"</code>&nbsp;<code style="overflow:auto; margin:0px!important; padding:0px!important; border:0px!important; outline:0px!important; font-size:1em!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; float:none!important; vertical-align:baseline!important; position:static!important; left:auto!important; top:auto!important; right:auto!important; bottom:auto!important; height:auto!important; width:auto!important; line-height:1.1em!important; min-height:auto!important; background:none!important">_ i);</code></td> 
  </tr> 
 </tbody> 
</table>

C99 引入了对参数个数可变的函数式宏的正式支持。在宏 “原型” 的末尾加上符号 … (就像在参数可变的函数定义中), 宏定义中的伪宏 \_\_VA\_ARGS\_\_ 就会在调用是 替换成可变参数。

最后, 你总是可以使用真实的函数, 接受明确定义的可变参数

如果你需要替换宏, 使用一个 函数和一个非函数式宏, 如 \#define printf myprintf

自定义调试信息的输出

调试信息的输出方法有很多种,  例如直接用printf,  或者出错时使用perror, fprintf等将信息直接打印到终端上, 在Qt上面一般使用qDebug，而守护进程则一般是使用syslog将调试信息输出到日志文件中等等...

使用标准的方法打印调试信息有时候不是很方便,  例如Qt编程, 在调试已有的代码时, 我想在打印调试信息的地方, 把代码位置也打印出来以方便定位错误, 或者需要在调试信息前面加一个前辍, 好方便在调试信息太多的时候可以用grep过滤一下, 仅显示本模块的调试信息, 这时就需要一个一个地修改已有的qDebug, 使其成为以下形式:  
　　qDebug( "\[模块名称\] 调试信息  File:%s, Line:%d", \_\_FILE\_\_, \_\_LINE\_\_ );  
　　这样的修改比较烦人, 而且一不小心会遗漏某个没改的...

为了能方便地管理调试信息的输出，一个比较简单的方法就是自已定义一个打印调试信息的宏, 然后替换原来的，废话就不多说了，直接给出一个现成的，下面是一个例子, 我用WiFi表示当前代码的模块名称，我要求在模块中的所有调试信息前面均带有\[WiFi\]前辍，这样我就能方便地只需使用命令行 | grep "\\\[WiFi\\\]"来过滤掉来自其它模块的调试信息了:

\#define qWiFiDebug(format, ...) qDebug("\[WiFi\] "format" File:%s, Line:%d, Function:%s", \#\#\_\_VA\_ARGS\_\_, \_\_FILE\_\_, \_\_LINE\_\_ , \_\_FUNCTION\_\_);

上面的宏是使用qDebug输出调试信息，在非Qt的程序中也可以改为printf，守护进程则可以改为syslog等等...  其中，决窍其实就是这几个宏 \#\#\_\_VA\_ARGS\_\_, \_\_FILE\_\_, \_\_LINE\_\_ 和\_\_FUNCTION\_\_,下面介绍一下这几个宏:

1)  \_\_VA\_ARGS\_\_ 是一个可变参数的宏，很少人知道这个宏，这个可变参数的宏是新的C99规范中新增的，目前似乎只有gcc支持（VC6.0的编译器不支持）。宏前面加上\#\#的作用在于，当可变参数的个数为0时，这里的\#\#起到把前面多余的","去掉的作用,否则会编译出错, 你可以试试。  
　　2) \_\_FILE\_\_ 宏在预编译时会替换成当前的源文件名  
　　3) \_\_LINE\_\_宏在预编译时会替换成当前的行号  
　　4) \_\_FUNCTION\_\_宏在预编译时会替换成当前的函数名称

有了以上这几个宏，特别是有了\_\_VA\_ARGS\_\_ ，调试信息的输出就变得灵活多了。  
　　有时，我们想把调试信息输出到屏幕上，而有时则又想把它输出到一个文件中，可参考下面的例子：

//debug.c

\#include <stdio.h>  
\#include <string.h>

//开启下面的宏表示程序运行在调试版本, 否则为发行版本, 这里假设只有调试版本才输出调试信息  
\#define \_DEBUG

\#ifdef \_DEBUG  
    //开启下面的宏就把调试信息输出到文件，注释即输出到终端  
    \#define DEBUG\_TO\_FILE  
    \#ifdef DEBUG\_TO\_FILE  
        //调试信息输出到以下文件  
        \#define DEBUG\_FILE "/tmp/debugmsg"  
        //调试信息的缓冲长度  
        \#define DEBUG\_BUFFER\_MAX 4096  
        //将调试信息输出到文件中  
        \#define printDebugMsg(moduleName, format, ...) \{\\  
            char buffer\[DEBUG\_BUFFER\_MAX+1\]=\{0\};\\  
            snprintf( buffer, DEBUG\_BUFFER\_MAX \\  
                    , "\[%s\] "format" File:%s, Line:%d\\n", moduleName, \#\#\_\_VA\_ARGS\_\_, \_\_FILE\_\_, \_\_LINE\_\_ );\\  
            FILE\* fd = fopen(DEBUG\_FILE, "a");\\  
            if ( fd != NULL ) \{\\  
                fwrite( buffer, strlen(buffer), 1, fd );\\  
                fflush( fd );\\  
                fclose( fd );\\  
            \}\\  
        \}  
    \#else  
        //将调试信息输出到终端  
        \#define printDebugMsg(moduleName, format, ...) \\  
                  printf( "\[%s\] "format" File:%s, Line:%d\\n", moduleName, \#\#\_\_VA\_ARGS\_\_, \_\_FILE\_\_, \_\_LINE\_\_ );  
    \#endif //end for \#ifdef DEBUG\_TO\_FILE  
\#else  
    //发行版本，什么也不做  
    \#define printDebugMsg(moduleName, format, ...)  
\#endif  //end for \#ifdef \_DEBUG

int main(int argc, char\*\* argv)  
\{  
    int data = 999;  
    printDebugMsg( "TestProgram", "data = %d", data );  
    return 0;  
\}

上面也说了，只有支持C99规范的gcc编译器才有\_\_VA\_ARGS\_\_这个宏，如果不是gcc编译器，或者所用的gcc编译器版本不支持\_\_VA\_ARGS\_\_宏怎么办？ 可参考下面的代码片段，我们换一种做法，可先将可变参数转换成字符串后，再进行输出即可:

void printDebugMsg( const char\* format, ...)  
\{  
    char buffer\[DEBUG\_BUFFER\_MAX\_LENGTH + 1\]=\{0\};

va\_list arg;  
    va\_start (arg, format);  
    vsnprintf(buffer, DEBUG\_BUFFER\_MAX\_LENGTH, format, arg);  
    va\_end (arg);

printf( "%s", buffer );  
\}

[http_www.cnblogs.com_alexshi_archive_2012_03_09_2388453.html]: http://www.eeban.com/?fromuid=1500484