linux-kernel - Re: question for C preprocessor wizards

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Message-ID: <4c5d.4a687cd4.a6013@altium.nl>
Date:	Thu, 23 Jul 2009 15:08:04 -0000
From:	dick.streefland@...ium.nl (Dick Streefland)
To:	linux-kernel@...r.kernel.org
Subject: Re: question for C preprocessor wizards

"Chris Friesen" <cfriesen@...tel.com> wrote:
| 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

You cannot generate preprocessing directives with macro expansion.
An alternative is to use a generic wrapper macro, and use that to
define wrappers for the functions. Something like:

#if FLAG
#define generic_wrapper(func, args...) \
        do { \
                dostuff(); \
                func(args); \
                do_more_stuff(); \
        } while (0)
#else
#define generic_wrapper(func, args...) func(args)
#endif

#define func1_wrapper(args...) generic_wrapper(func1, args)
#define func2_wrapper(args...) generic_wrapper(func2, args)
#define func3_wrapper(args...) generic_wrapper(func3, args)
...

-- 
Dick Streefland                      ////                      Altium BV
dick.streefland@...ium.nl           (@ @)          http://www.altium.com
--------------------------------oOO--(_)--OOo---------------------------

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