Variably modified array at file scope

Question

I want to create a constant static array to be used throughout my Objective-C implementation file similar to something like this at the top level of my ".m" file:

static const int NUM_TYPES = 4;
static int types[NUM_TYPES] = { 
  1,
  2, 
  3, 
  4 };

I plan on using NUM_TYPES later on in the file so I wanted to put it in a variable.

However, when I do this, I get the error

"Variably modified 'types' at file scope"

I gather that this may have something to do with the array size being a variable (I don't get this message when I put an integer literal there, like static int types[4]).

I want to fix this, but maybe I am going about it all wrong...I have 2 goals here:

1. To have an array which is accessible throughout the file
2. To encapsulate NUM_TYPES into a variable so I don't have the same literal scattered about different places in my file

Any suggestions?

[EDIT] Found this in the C Faq: http://c-faq.com/ansi/constasconst.html

Answer 1

The reason for this warning is that const in c doesn't mean constant. It means "read only". So the value is stored at a memory address and could potentially be changed by machine code.

Answer 2

If you're going to use the preprocessor anyway, as per the other answers, then you can make the compiler determine the value of NUM_TYPES automagically:

#define NUM_TYPES (sizeof types / sizeof types[0])
static int types[] = { 
  1,
  2, 
  3, 
  4 };

Answer 3

#define NUM_TYPES 4