Question

I got this macro that posts events to some event-queue.

POST_(myTarget, event)

The event may either be posted directly to a local queue or may be serialized and posted to the event-queue of a I2C service which sends the event to another microcontroller. Whether the receiving service is local or remote is defined like:

#define myTarget_REMOTE
#define anotherTarget_LOCAL

What I want to do is something like this (which is certainly not allowed):

#define POST(target, e) \
    #ifdef target##_REMOTE \
        /* create a i2c request-event with serialized(e) 
           as parameter and post to I2c-Manager */
    #else \
        /* post directly */
        POST_(target, event) \
    #endif

So, all the information is there at compile time, but I don’t know how to tell the preprocessor what to do.

• I could create two macros for each target depending on its local/remote define, but this would be messy.
• I could do the test at runtime, but this would be a sad story also.

EDIT:

An example how the program will look like clearer:

#define target1_LOCAL
#define target2_REMOTE

POST(target1, e) ==preprocessor==> POST_(target1, e)

POST(target2, e) ==preprocessor==> 
    do { \
        req = createI2cRequest(serialize(e)); \
        POST_(I2cManager, req); \
    }while(0)

So, in the program I just use POST(target, event) and the location of the target is completely transparent.

Answer 1

So i finally figured it out.
The trick is to use the preprocessor to give the compiler all needed information and rely on the compiler to optimize the if/else away.

#define REMOTE  1
#define LOCAL   0

#define TARGET0_LOCATION REMOTE
#define TARGET1_LOCATION LOCAL

#define TEST(target) do { \
        if(target##_LOCATION == REMOTE) printf("REMOTE\n"); \
        else printf("LOCAL\n"); \
    }while(0)

main(){
    TEST(TARGET0);
    TEST(TARGET1);
}

Output:

REMOTE
LOCAL