如何使预处理器宏贪婪？ [英] How to make a preprocessor macro greedy?

问题描述

我们有以下预处理程序宏。它用于帮助Doxygen文档，因为Doxygen在C ++和某些模板typedef方面存在问题：

We have the following preprocessor macro. Its used to help with Doxygen documentation because Doxygen has troubles with C++ and some template typedefs:

#if defined(DOXYGEN_PROCESSING)
# define DOCUMENTED_TYPEDEF(x, y) class y : public x {};
#else
# define DOCUMENTED_TYPEDEF(x, y) typedef x y;
#endif

当 X 是非模板，或只有一个模板参数。但是，如果 X 是具有多个参数的模板：

It works great when X is a non-template or has only one template parameter. However, if X is a template with multiple parameters:

DOCUMENTED_TYPEDEF(Foo<R,S>,Bar);

然后由于字符串被拆分为 Foo< R而导致编译错误和 S>，Bar （并且不会生成文档）。

Then it results in compile errors because the string is split into Foo<R and S>,Bar (and it does not generate the documentation).

如何使预处理器宏贪婪？

How do I make a preprocessor macro greedy?

推荐答案

无法更改预处理器将参数解析为宏的方式。不在括号内的逗号始终会分隔宏参数。

There is no way to change how the preprocessor parses the arguments to a macro. Commas that are not within parentheses always separate macro arguments.

您可能可以执行的操作是

DOCUMENTED_TYPEDEF((Foo<R,S>), Bar);

当然，这只有在内部括号可以出现在宏扩展中的情况下才有效。我不记得我是否会在您显示的上下文中引起麻烦。

but of course this only works if it's okay for the inner parentheses to appear in the expansion of the macro. I don't remember off the top of my head if this will cause problems in the contexts you are showing.

如果可以使用C99可变参数宏，则可以使用它们可以消除多余的括号：

If it's OK to require C99 variadic macros, you can use them to get rid of the extra parentheses:

#define STRIP_PARENS(...) __VA_ARGS__
#if defined(DOXYGEN_PROCESSING)
# define DOCUMENTED_TYPEDEF(x, y) class y : public STRIP_PARENS x {};
#else
# define DOCUMENTED_TYPEDEF(x, y) typedef STRIP_PARENS x y;
#endif

DOCUMENTED_TYPEDEF((Foo<R,S>), Bar);

但是现在您总是必须在第一个参数是DOCUMENTED_TYPEDEF。

but now you always have to put an extra pair of parentheses around the first argument to DOCUMENTED_TYPEDEF.

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