Conditional macro #define for a function - causing: "function" redefined warning - gcc

Question

I just saw this thread, describing how to add conditional macros:
Conditional value for a #define
but in my case I am defining a function within the condition.
#if TARGET_IPHONE_SIMULATOR
#define doSomething(){\
\\ does something
}\
#else
#define doSomething(){\
\\ does something else
}\
#endif
This does work, except I is causing gcc compiler to throw this warning:
"doSomething" redefined
This is the location of the previous arguments
Is there any workaround to help getting rid of the warnings?
UPDATE:
So I tried including the condition inside my definition:
#define doSomething(){\
#if TARGET_IPHONE_SIMULATOR
\\ do something
#else
\\ do something else
#endif
}\
but that throws an error:
error: '#' is not followed by a macro parameter.

Answer 1

I found the answer to my question here.
Conclusion:
you cannot include #ifdef etc... inside #define, because there should only be one pre-processing directive per line.
So although we can break the line with a backslash '\' this helps writing readable multiline macros,
but the preprocessor will see it as one line:
#define doSomething(){ #if TARGET_IPHONE_SIMULATOR ... #endif }
Which throws this error:
error: '#' is not followed by a macro parameter.
That makes sense, so I will have to rethink my implementation.

Answer 2

There is a quirk in your thinking which is by analogy/ extension. doSomething() has to be viewed as a function-like macro. As such its definition is ambivalent. Zoom out and see below:
doSomething() {
#if TARGET_IPHONE_SIMULATOR
// conditionally compiled code
#else
// platform-specific code
#endif
}

Answer 3

Also, this might address the error you received:# and ## have special purposes inside macro definitions. # is used to surround a macro parameter with double quotes. ## is used to concatenate two macro parameters. Example:#define ABC(X) #XABC(hello) results in "hello".#define XYZ(X,Y) X##YXYZ(O,K) results in OK.
Note that this feature is (possibly) unique to ANSI C.
Also, why would you be using a macro like this? Might a function work better for you?

Answer 4

One option to consider is creating a condition in a macro that will resolve at compile time. Consider the following:
If I would like to call a different function based on the value of 'c' as a pre-processor action, I can define a macro that checks the value of 'c' statically.
#define AorB(c) ((c>0) ? (Do_A(c)) : (Do_B(c)))
Then if you configure a level of optimization that removes branches that are never reachable, it should strip out which ever case wasn't performed. This may not exactly be what you were looking for.