reversing a macro

Deepak Inbasekaran · 07-20-2006, 12:27 AM

i have a macro defined as

Quote:

#define CARD 1

now if i want to do the reverse , is there any options like if i get "1" as input it must be printed as "CARD"

(any idea, other than using arrays )

jlinkels · 07-20-2006, 06:17 AM

What you you do if you have:

Code:

#define CARD 1
#define KEY 1

AFAIK as I know there is not simple way to do it. I faced this problam once as I had a few hundred of these values defined, and I wanted the user to be able to use these names in a config file, and recongnize them in my program.

Since these macros are only known by the compiler I had to maintain a list of name/value combinations. For this I wrote a little parser to parse thru the appropriate files and find the combinations.

If you don't want to use an array, try a linked list, I think that was what I did.

jlinkels

osor · 07-20-2006, 11:34 AM

No you can't. This is not the way macros were meant to be used.

xhi · 07-20-2006, 01:11 PM

Quote:

Originally Posted by Deepak Inbasekaran

i have a macro defined as

now if i want to do the reverse , is there any options like if i get "1" as input it must be printed as "CARD"

(any idea, other than using arrays )

other than arrays?

switch, or if

xhi · 07-20-2006, 01:18 PM

i guess if it was c++ you could use STL, for example std::map..

Deepak Inbasekaran · 07-20-2006, 09:54 PM

i got this solution and its working fine

Quote:

#include <stdio.h>
#define str(s) #s

#define LINE 1

int main()
{
printf("%s", str(LINE));
}

graemef · 07-21-2006, 12:41 AM

So what does your solution actually do?

there are two macros defined, the first defines a function called str() and the other defines an identifier called LINE.

The preprocessor will then modify your code according to the defined macros, it will see the str macro and replace it, giving you:

Code:

#include <stdio.h>

int main()
{
printf("%s", "LINE");
}

There is no occurence of the identifier LINE for the preprocessor to modify and so it will be ignored. As others have said you are going to have to build a switch (for example) to actually reverse the macro.

I'm not entirely sure why you want to do that. There is probably a better way to address the problem, and I don't understand why you don't want to use an array, again that is because I don't understand what (at the end of the day) it is you are trying to achieve.