how to concat a space with a symbol using c macro

Question

#define var(N) variable ## N

var(1) got variable1

I want to get variable, how can I define the macro?

var( ) works, but it always give a warning. is there any other solutions?

Please add the warning, and the line thats producing the warning — thelaws, Feb 27 '15 at 15:18
@HuStmpHrrr it is an example, currently I am trying to rewrite some old code — camino, Feb 27 '15 at 15:22
@camino Do you want both `var(1)` and `var()` to work? Where the latter should expand to just `variable?`, making the macro argument optional? — unwind, Feb 27 '15 at 15:23
@unwind if var(1) can return "variable" is also fine. for example , I want var(1) ==>variable, var(2) ==>variable2, var(3) ==>variable3, — camino, Feb 27 '15 at 15:31
clang doesn't warn either with `-Wall -Wextra -pedantic`. What are you using? — Alex Celeste, Feb 27 '15 at 15:36
Reopening the question, since other than the answer in the linked question claims, C and C++ **are** different in the preprocessor. Also the version of C or C++ plays a role. — Jens Gustedt, Feb 27 '15 at 16:12

score 2 · Accepted Answer · answered Feb 27 '15 at 16:15

2

In fact the version that you presented always needs a non-empty argument for N. If you have a modern C compiler you can use this construct:

#define var(...) variable ## __VA_ARGS__

This accepts empty arguments and you should be fine.

"modern" here means C as of 1999.

answered Feb 27 '15 at 16:15

Jens Gustedt

Notes on this answer: you must be using a C99 compiler (-std=c99 in gcc) or at least one that supports variadic macros. ## is the concatenation operator in the C preprocessor. – Tyler Durden Feb 27 '15 at 16:47

unwind · Answer 2 · 2015-02-27T15:24:24.103

-2

Don't use the argument inside the macro:

#define var(n) variable

edited Feb 27 '15 at 15:24

answered Feb 27 '15 at 15:18

unwind

2

I guess the op would like to preserve the concatenation functionality – Eugene Sh. Feb 27 '15 at 15:19
@EugeneSh. Oh. Thanks, I didn't understand it correctly, then. – unwind Feb 27 '15 at 15:23

2 Answers2