How to access GCC -Dmacro?

Question

The question is as the title, I'm compiling a quite big code and want to have a debug option only when compiled with such option.

I'm using make to compile and I add the compile option on my debug rule:

debug: main
$(eval CFLAGS := -D_DEBUG_)

What I could not do was use this _DEBUG_ macro inside the code to then print some debug info.

Note that you should not, in general, create function, variable, tag or macro names that start with an underscore. Part of [C11 §7.1.3 Reserved identifiers](https://port70.net/~nsz/c/c11/n1570.html#7.1.3) says: — _All identifiers that begin with an underscore and either an uppercase letter or another underscore are always reserved for any use._ — _All identifiers that begin with an underscore are always reserved for use as identifiers with file scope in both the ordinary and tag name spaces._ See also [What does double underscore (`__const`) mean in C?](https://stackoverflow.com/q/1449181) — Jonathan Leffler, Nov 10 '20 at 17:20
What do you mean by "I could not do"? Did the compiler issue an error? Please always include the actual system message(s) of your problem as described in [MCVE]. — Vroomfondel, Nov 11 '20 at 12:53

score 4 · Answer 1 · answered Nov 10 '20 at 16:27

Passing -Dmacro to a compiler is equivalent to defining this symbol in the code:

#define macro

So "using" it in the code is similar as well - you can use preprocessor conditional directives:

#ifdef macro
// Your conditional code
#endif

(in your specific case the symbol name is _DEBUG_)

1 Answers1