Why can't I use an NSInteger in a switch statement?

Question

Why doesn't this work:

NSInteger sectionLocation = 0;
NSInteger sectionTitles = 1;
NSInteger sectionNotifications = 2;

switch (section) {
    case sectionLocation:
        //
        break;
    case sectionTitles:
        //
        break;
    case sectionNotifications:
        // 
        break;
    default:
        //
}

I get this compile error:

error: case label does not reduce to an integer constant

Is it not possible to use NSInteger's like this? If so, is there another way to use variables as cases in a switch statement? sectionLocation etc. have variable values.

Lilley

Answer 1

The problem isn't the scalar type, but that the case labels may change value when they are variables like that.

For all intents and purposes, the compiler compiles a switch statement as a set of gotos. The labels can't be variable.

Use an enumerated type or #defines.

Benjamin

Answer 2

The reason is that the compiler will often want to create a 'jump table' using the switch value as the key into that table and it can only do that if it's switching on a simple integer value. This should work instead:

#define sectionLocation  0
#define sectionTitles  1
#define sectionNotifications 2

int intSection = section;

switch (intSection) {
    case sectionLocation:
        //
        break;
    case sectionTitles:
        //
        break;
    case sectionNotifications:
        // 
        break;
    default:
        //
}

Livingston

Answer 3

The problem here is you are using variables. You can only use constants in switch statements.

Do something like

#define SOME_VALUE 1

or

enum Values {
    valuea = 1,
    valueb = 2,
    ...
}

And you will be able to use valuea and so forth in your switch statement.

Phillada

So I'll have to resort to if-else-if-else again? Isn't there a way around this? – Lilley

Yes, use defines, whats the problem with that? :D – Phillada

Answer 4

If your case values truly change at runtime, that's what the if...else if...else if construct is there for.

Bremble

Answer 5

or just do this

switch((int)secion)

Rascally