replacing #define

Question

Hi, i want to replace a

#define INTERVAL_MASK(b) (1 << (b))

with a inline function.

int INTERVAL_MASK(int b)
{
    return (1 << b);
}

But i have a switch case, which uses the preprocessor directive in case statements. How to go about converting this? Replacing the switch with if is the only option?

Thanks, gokul.

Answer 1

Why not const int interval_mask = (1 << b);?

Answer 2

The switch case label must have an integral constant expression, so you can't have a function call in the case label.

There is nothing wrong with using a macro for this.

If you are really concerned about using the macro, #define it just before the switch statement and #undef it immediately after the switch statement.

In C++0x, you'll be able to create constexpr functions that can be used in constant expressions, but to the best of my knowledge no compiler actually fully supports that part of C++0x yet.

Answer 3

An important thing to note about the switch statement is that the case values may only be constant integral expressions.

The only workaround I can think for you, is a bunch of if-else statements. Or, you could just generate the cases from 2 (1 << 1) to 1024 (1 << 10) or to whatever your limit is, programmatically. Means your switch statement will look like:

switch(i) {
    case 2:
        //random stuff
        break;
    ...
    case 1024:
        //random
        break;
    ...
}

There would be a separate code that will generate this. It won't be that hard actually.

Answer 4

as far as I know, functions containing control statements like switch, if and loops are not inlined.

You can be sure if you use a macro.