linux-kernel - Re: question for C preprocessor wizards

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Message-ID: <20090723010715.GA5712@cr0.nay.redhat.com>
Date:	Thu, 23 Jul 2009 09:07:15 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: question for C preprocessor wizards

On Wed, Jul 22, 2009 at 12:50:49PM -0600, Chris Friesen wrote:
>
>I'm hoping someone can help me out.


This is _not_ a question about kernel. :)

>
>I've got a bunch of code that call a bunch of different wrapper
>routines, with varying numbers of arguments.  Depending on whether a
>compile flag is set, I want to do some stuff before and after calling
>the "real" routine.  I can do this easily enough with a macro.
>
>#if FLAG
>#define func_wrapper(args...) \
>	do { \
>		dostuff(); \
>		func(args); \
>		do_more_stuff(); \
>	} while (0)
>#else
>#define func_wrapper(args...) func(args)
>#endif
>
>
>However, given that there are hundreds of functions, I'd like to
>generate these macros with another macro, sort of like:
>
>#if FLAG
>#define WRAPPER(func) \
>	#define func # _wrapper(args...) \
>	do { \
>		dostuff(); \
>		func(args); \
>		do_more_stuff(); \
>	} while (0)
>#else
>#define WRAPPER(func) \
>	#define func ## _wrapper(args...) func(args)
>#endif
>
>Where I could then do
>
>WRAPPER(func1)
>WRAPPER(func2)
>...
>WRAPPER(func100)
>
>
>However, the preprocessor complains about having that "#" in the macro
>body where it isn't used for stringification.
>
>
>Anyone have any ideas how to accomplish this?  I had considered writing
>an app to programmatically generate an include file as a precursor to
>actually compiling the real app, but I was hoping there was a more
>elegant solution.

Well, you can define func() as a real function instead of a macro,
i.e:

#define WRAPPER(func) \
 void func ## _wrapper(args, ...) \
 {  \
    dostuff(); \
    func(args); \
    do_more_stuff(); \
 }


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