Assign a value to a variable at compilation time

Question

I'd like to assign a specific value to a variable when my code is compiling (for C and C++):

For example having :

//test.c
int main()
{
   int x = MYTRICK ; (edit: changed __MYTRICK__ to MYTRICK to follow advices in comment)
   printf ("%d\n", x);

   return 0;
}

beeing able to do something like:

gcc -XXX MYTRICK=44 test.c -o test

and having as a result :

$./test
44

Answer 1

Use -D option:

gcc -DMYTRICK=44 test.c -o test

And use MYTRICK macro in your program and not __MYTRICK__. Names beginning with __ are reserved by the implementation.