Conditional macro expansion
- by Dave DeLong
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 with arguments: %@, %@, %@", @"arg1", @"arg2", @"arg3"), and that will get expanded into a more complex method invocation that includes things like self, _cmd, __FILE__, __LINE__, etc, so that I can easily track where things are getting logged. This works great.
Now I'd like to expand my macros to not only work with Objective-C methods, but general C functions. The problem is the self and _cmd portions that are in the macro expansion. These two parameters don't exist in C functions. Ideally, I'd like to be able to use this same set of macros within C functions, but I'm running into problems. When I use (for example) my Log() macro, I get compiler warnings about self and _cmd being undeclared (which makes total sense).
My first thought was to do something like the following (in my macro):
if (thisFunctionIsACFunction) {
DoLogging(nil, nil, format, ##__VA_ARGS__);
} else {
DoLogging(self, _cmd, format, ##__VA_ARGS__);
}
This still produces compiler warnings, since the entire if() statement is substituted in place of the macro, resulting in errors with the self and _cmd keywords (even though they will never be executed during function execution).
My next thought was to do something like this (in my macro):
if (thisFunctionIsACFunction) {
#define SELF nil
#define CMD nil
} else {
#define SELF self
#define CMD _cmd
}
DoLogging(SELF, CMD, format, ##__VA_ARGS__);
That doesn't work, unfortunately. I get "error: '#' is not followed by a macro parameter" on my first #define.
My other thought was to create a second set of macros, specifically for use in C functions. This reeks of a bad code smell, and I really don't want to do this.
Is there some way I can use the same set of macros from within both Objective-C methods and C functions, and only reference self and _cmd if the macro is in an Objective-C method?
