#redefine preprocessor macro statement.

[Ernie.Pasveer@cggveritas.com]

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]

Re: #redefine preprocessor macro statement.

On Apr 14, 1:00 pm, Ernie.Pasv...@c ggveritas.com 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_funct ion(char *thing)
{
/* Do stuff here */
}


isolating_funct ion("orange");
isolating_funct ion("banana");
isolating_funct ion("apple");

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

[Kenneth Bull]

Re: #redefine preprocessor macro statement.

On Apr 14, 4:00 pm, Ernie.Pasv...@c ggveritas.com 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]

Re: #redefine preprocessor macro statement.

Kenneth Bull <kenneth.bull@g mail.comwrites:

On Apr 14, 4:00 pm, Ernie.Pasv...@c ggveritas.com 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_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"