Alter function name using #define

Question

Could I implement this in C?

#define X abc

then X_menu(); will be preprocessed as abc_menu();

In another build if I define X def then X_menu(); will be def_menu();

I'm sure there should be a method, but I could not figure out.

If users could do this then internal details of standard libraries would need to be named __l__i__k__e__t__h__i__s and also I would want to strangle people. Actually even that wouldn't work ... standard libraries would be impossible to implement safely. — Jonathan Wakely
– Jonathan Wakely, Commented Dec 15, 2014 at 20:29
The usual convention is not to play such tricks with the preprocessor. Even the (working) answer by Ryan Haining should not be used: The indirection adds a big speedbump for the reader, and the savings in typing is minimal. If you must some kind of automatic tool to shortcut your typing, use editior abbreviations. Learning to touch-type helps as well. — cmaster - reinstate monica
– cmaster - reinstate monica, Commented Dec 15, 2014 at 20:41
@user1932637 what I gave you works but is a bad idea to actually use — Ryan Haining
– Ryan Haining, Commented Dec 15, 2014 at 21:50

Community · Accepted Answer · 2017-05-23 11:44:04Z

4

No, you wouldn't want this behavior as it would be very unsafe and difficult to deal with replacing every X in every name. However, you could use a macro function to do something similar

#define X(F) abc##F
X(_menu();)

## is macro concatenation, so X(_menu();) will expand to abc_menu();

As Roger points out, the macro will also work with the syntax

X(_menu)();

which you may find easier to read

edited May 23, 2017 at 11:44

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answered Dec 15, 2014 at 20:15

Ryan Haining

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3 Comments

Roger Lipscombe Over a year ago

X(_menu)(); is easier on the eye, imo.

xian Over a year ago

Ha, it's tricky. cool! the only thing I don't like is you have to define X(F) rather than X. is there another to solve it?

Ryan Haining Over a year ago

@user1932637 afaict, nothing nicer than this while still only using the preprocessor, if you start doing your own code generation then the possibilities are endless

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