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cmacrosvariadic-macros

C macro expansion of a function pointer based on for loop incrementor

I have a function that takes a pointer to a function as a parameter. This function get's called within a for loop due to the similar nature of the names of the function pointer I use a macro to expand the name into the function. IT looks something like this:

void fill(int, int(*funcbase)(int));
int funcbase0(int);
int funcbase1(int);
int funcbase2(int);
int funcbase3(int);
/// all the way through funcbase31

#define FILL_(num) fill(num, funcbase##num)
#define FILL(num) FILL_(num)

for(int i = 0; i < 32; i++)
    FILL(i);

I would like this to call fill for 0,1,2,... and funcbase0, funcbase1, funcbase2,... , but it calls fill with the second parameter of "funcbasei" It does not expand i every time.

Is what I'm trying to do possible? What compiler would I need to try? (I'm using gcc 4.9.3)

Solution

  • What you are trying to do is not possible with a macro because macros are expanded at compile time, well before the runtime and loops start running.

    However, you can easily do this with a for loop on an array of function pointers:

    typedef int(*funcbase_t)(int);
funcbase_t fbases[] = {
    funcbase0, funcbase1, funcbase2, funcbase3, ...
};

    Now you can run your loop on fbase array:

    for(int i = 0; i < 32; i++)
    fbases[i](i);