question for C preprocessor wizards

question for C preprocessor wizards

[Chris Friesen]

I'm hoping someone can help me out.

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.

Thanks,

Chris

Re: question for C preprocessor wizards

[Amerigo Wang]

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(); \
 }

Re: question for C preprocessor wizards

[Bernd Petrovitsch]

On Thu, 2009-07-23 at 09:07 +0800, Amerigo Wang wrote:
> 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.
One can't generate preprocessor directive via #define.

> >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.
Personally, I don't find it in elegant to generate simple/trivial .c
or .h files with some small-ish perl/shell-script via sane Makefile
rules. Perhaps unless the contents is (almost) never going to change
(and even then there might be good reasons).
Within the kernel, it's probably better to avoid perl-scripts for easier
acceptance.

> 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(); \
>  }
ACK.

Or the other way around:
Have dostuff() at the begin and do_more_stuff() at the end of the real
function in the source and #if-them-away per
----  snip  ----
#if FLAG
void dostuff();
void do_more_stuff();
#else
#define dostuff() ((void)0)
#define do_more_stuff() ((void)0)
#endif
----  snip  ----

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: question for C preprocessor wizards

[Dick Streefland]

"Chris Friesen" <cfriesen@nortel.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@altium.nl           (@ @)          http://www.altium.com
--------------------------------oOO--(_)--OOo---------------------------