Constant Definition within Constant Definition in C

Question

I'm trying to use a constant definition in another constant definition like so:

#define ADDRESS 5002
#define FIND "foundaddress ADDRESS"

But this includes ADDRESS in the FIND constant when I want the constant FIND to be foundaddress 5002.

Is there any way to do this?

Try `#define FIND "found address"ADDRESS` – Dan Pichelman Apr 18 '13 at 19:08 — Dan Pichelman, Apr 18 '13 at 19:08

score 2 · Answer 1 · answered Apr 18 '13 at 19:13

If you don't mind changeing ADDRESS to a string, you can use the preprocessor concatenation

#define ADDRESS "5002" /* rather than 5002 without quotes */
#define FIND "foundaddress " ADDRESS

The compiler will see that 2nd line as

#define FIND "foundaddress 5002"

score 2 · Answer 2 · answered Apr 18 '13 at 19:13

You need to use the preprocessor stringification operator to make your value into a string, then concatenate them like others have said.

#define ADDRESS_TO_STRING(x) #x
#define ADDRESS 5002
#define FIND "foundaddress " ADDRESS_TO_STRING(ADDRESS)

And if that gives you "foundaddress ADDRESS", it means you need one more layer:

#define ADDRESS_TO_STRING_(x) #x
#define ADDRESS_TO_STRING(x) ADDRESS_TO_STRING_(x)
#define ADDRESS 5002
#define FIND "foundaddress " ADDRESS_TO_STRING(ADDRESS)

" if that gives you ..." -- It must if you're using a conforming C implelentation. — Jim Balter, Apr 18 '13 at 19:26

Halim Qarroum · Answer 3 · 2013-04-18T19:14:54.490

1

Yes.

#define ADDRESS "5002"
#define FIND "foundaddress " ADDRESS

edited Apr 18 '13 at 19:14

answered Apr 18 '13 at 19:09

Halim Qarroum

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For it to work in GCC I needed to `#define ADDRESS "5002"` though. – Kninnug Apr 18 '13 at 19:13

score 0 · Answer 4 · edited May 23 '17 at 11:43

From C/C++ Macro string concatenation

/*
 * Turn A into a string literal without expanding macro definitions
 * (however, if invoked from a macro, macro arguments are expanded).
 */
#define STRINGIZE_NX(A) #A

/*
 * Turn A into a string literal after macro-expanding it.
 */
#define STRINGIZE(A) STRINGIZE_NX(A)

Then

#define FIND ("foundaddress " STRINGIZE(ADDRESS))

produces ("foundaddress " "5002") which should be usable wherever you need a string literal, due to C's string literal concatenation.

Constant Definition within Constant Definition in C

4 Answers4