Conditional macro expansion

Question

Heads up: This is a weird question.

I\'ve got some really useful macros that I like to use to simplify some logging. For example I can do Log(@\"My message wi

Answer 1

You can use some sort of macro conditional:

#ifndef OBJECTIVE_C
  #define self 0
  #define _cmd ""
#endif

I'm not quite sure what you should define self and _cmd to, those were just guesses.

I'm not sure if there is a predefined macro that you can to check if you are compiling in Objective C so you may need to define OBJECTIVE_C manually as part of your build.

Answer 2

You can use

if defined "abc" <statement1>
else if defined "def" <statement2>

Answer 3

The preprocessor does all of its work before the actual code is parsed. The preprocessor cannot know whether a function is C or obj-C because it runs before the code is parsed.

For the same reason,

if (thisFunctionIsACFunction) {
  #define SELF nil
  #define CMD nil
} else {
  #define SELF self
  #define CMD _cmd
}
DoLogging(SELF, CMD, format, ##__VA_ARGS__);

cannot work - the #defines are processed before the compilation stage.

So, the code itself must contain a "runtime" check (though the compiler may optimise this out).

I would suggest defining something like

void *self = nil; //not sure about the types that
SEL _cmd = nil;   //would be valid for obj-c

at global scope; the C functions will "see" these definitions while the Objective-C methods will hopefully hide them with their own definitions.