#redefine preprocessor macro statement.

[Ernie.Pasveer]

Hi All,

Is there a way to create a macro called #redefine that will allow
redefinition without having to use #ifdef/#undef

For example, I'd like to do something like this :

#define THING "apple"
... code

#redefine THING "banana"
... code

#redefine THING "orange"
... code
Instead of :

#define THING "apple"
... code

#undef THING
#define THING "banana"
... code

#undef THING
#define THING "orange"
... code

[user923005]

On Apr 14, 1:00*pm, [e-mail] wrote:

Hi All,

Is there a way to create a macro called *#redefine that will allow
redefinition without having to use #ifdef/#undef

For example, *I'd like to do something like this :

* * #define THING *"apple"
* * ... code

* * #redefine THING "banana"
* * ... code

* * #redefine THING "orange"
* * ... code

Instead of :

* * #define THING *"apple"
* * ... code

* *#undef THING
* *#define THING "banana"
* * ... code

* *#undef THING
* *#define THING "orange"
* *... code

void isolating_function(char *thing)
{
/* Do stuff here */
}
isolating_function("orange");
isolating_function("banana");
isolating_function("apple");

I think that it is good that you cannot do what you want to do. It is
trouble waiting to happen.

[Kenneth Bull]

On Apr 14, 4:00*pm, [e-mail] wrote:

Hi All,

Is there a way to create a macro called *#redefine that will allow
redefinition without having to use #ifdef/#undef

For example, *I'd like to do something like this :

* * #define THING *"apple"
* * ... code

* * #redefine THING "banana"
* * ... code

* * #redefine THING "orange"
* * ... code

just change the #redefine's to #define's

>
Instead of :

* * #define THING *"apple"
* * ... code

* *#undef THING
* *#define THING "banana"
* * ... code

* *#undef THING
* *#define THING "orange"
* *... code

You don't need the #undef before reusing the #define.

[Keith Thompson]

Kenneth Bull <ke**********@gmail.comwrites:

On Apr 14, 4:00*pm, [e-mail] wrote:

>Is there a way to create a macro called *#redefine that will allow
redefinition without having to use #ifdef/#undef

For example, *I'd like to do something like this :

* * #define THING *"apple"
* * ... code

* * #redefine THING "banana"
* * ... code

* * #redefine THING "orange"
* * ... code

No, there isn't. A macro expansion cannot include preprocessor
directives.

just change the #redefine's to #define's

[...]

You don't need the #undef before reusing the #define.

Yes, you do. C99 6.10.3p2 says:

An identifier currently defined as an object-like macro shall not
be redefined by another #define preprocessing directive unless the
second definition is an object-like macro definition and the two
replacement lists are identical.

followed by similar wording for function-like macros.

I see this was cross-posted to comp.lang.c and comp.lang.c++. I
assume the rules for C++ are similar, but I'm not certain. It's
better to post to the newsgroup that covers the language you're
actually using.

--
Keith Thompson (The_Other_Keith) <ks***@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"