在不识别##的编译器上在可变宏上吞吐逗号 [英] Swallowing comma in variadic macros on compilers that do not recognise ##

问题描述

在gcc中，可以通过添加逗号，例如，## ____ VA_ARGS ____ ，如 Variadic宏但是，我的编译系统中的编译器（超出我的控制范围）并不理解，## $ b / code>语法，所以不会吞下逗号。

有没有可以使用的解决方法？

谢谢！

解决方案

是的，gcc吞咽逗号并不标准，您不应该依赖它。

使用符合C99标准的预处理器，您可以通过测试一个空标记的宏参数来获得类似的效果。有关这项工作的想法，您可以在这里，对于一整套预处理宏来说，可以轻松编程这些功能，这里有 P99 。

I need to write a variadic macro in C which must take zero or more arguments.

In gcc, that can be achieved by adding "##" after the comma, e.g. ,##____VA_ARGS____ as answered in Variadic macros with zero arguments.

However, the compiler in my build system (beyond my control) does not understand the ,## syntax and so does not swallow the comma.

Is there a workaround I can use?

Thanks!

解决方案

Yes, gcc swallowing the comma is non standard and you should not rely on that.

With C99 conforming preprocessors you may achieve a similar effect by testing for a macro arguments that is the empty token. For the ideas of how this works you could see here, for a whole set of preprocessor macros that ease the programming of such features there is P99.

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