How to make the C++ precompiler do a "loop"

Question

I want to simplify the following code:

switch (index)
    {
    case 1:
        output = function1();
        break;
    case 2:
        output = function2();
        break;
    case 3:
        output = function3();
        break;
    ....

Where index is a compile time constant.

If I would use a precompiler macro, I would need to use it n times, where n is the number of cases. How can I reduce the above mentioned code to O(1) lines of code?

Answer 1

May be supermacro can slightly simplify your work. Simply create "counter.def" file with code:

COUNTER(1)
COUNTER(2)
COUNTER(3)
#undef COUNTER

Then in any case of using switch or any other construction with repeating counting

switch(index)
{
    #define COUNTER(i) case i: output = function##i(); break;
    #include "counter.def"
}