Compact version for defining a macro if undefined

Question

I'm currently writing a set of modules with parameters that can be defined at compile time. For each value, I'm also specifying a default value, so that a user only needs to define those values they want to change. There is a user-defined include file, which contains the #define macros with the overwritten values.

In my module, I'm using

#include "user-defines.h"
#include "module.h"

where module.h contains the default definitions.

Currently, I'm using the following pattern for defining the default values in module.h

#ifndef somemacro
#define somemacro "default value"
#endif

which works, but means a lot of extra typing. It is also three lines instead of one, blowing up the source code.

My question is, is there a more elegant way (e.g. 1 line, not repeating the macro name) to define the default value only in case it is undefined?

I experimented with a macro `DEFAULT(x,y)` that writes macro code but could not get it to work. — Peter B., Dec 13 '20 at 00:22
It doesn't get more compact than three lines. No, you can't use a macro to write a new macro. — Jonathan Leffler, Dec 13 '20 at 00:26
You can write a script to create the header file from a simpler file. Or you can do it with Find/Replace in your editor. But there's nothing built into C for it. — Barmar, Dec 13 '20 at 00:28
Secondly redefining the macro is an indication of the wrong project structure — 0___________, Dec 13 '20 at 00:50

Compact version for defining a macro if undefined

0 Answers0