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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: do { quit; } else { }
Date: Wed, 9 Apr 2025 14:54:05 +0200
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On 09/04/2025 11:00, Ike Naar wrote:
> On 2025-04-08, bart <bc@freeuk.com> wrote:
>> However if I need to initialise the variable:
>>
>>      extern int table[];          // shared
>>      int table[] = (10, 20, 30)
>>
>> then other modules can't pick up length of the array.
> 
>    extern int table[3];

That is fine if you know the size in advance of initialisation.  Very 
often, of course, you /do/ know the size - especially when talking about 
data shared directly between translation units.  (And if it is not 
shared, you don't declare it in a header.)

An array really needs two bits of information - a way to find the first 
element, and the number of elements.  (There are also other bits of 
compile-time data such as the type.)  In C, these two things are not 
tightly joined - you typically have to pass them separately when 
exchanging information about an array.  This means you get maximal 
efficiency - you don't need to pass around information that you have no 
use of or know from somewhere else.  But it also means you need a little 
extra effort in the code when you need them both.

For example, you can have :

// unit.h
extern int table[];
extern const int table_count;


// unit.c
#include "unit.h"

int table = [10, 20, 30};
const int table_count = sizeof(table) / sizeof(table[0]);