OpenEuphoria

Re: 0-based Indexing

• Posted by Christian.CUVIER at agriculture.gouv.fr Jul 17, 2003
• 498 views

> From: gertie at visionsix.com
> Subject: Re: 0-based Indexing
> 
> 
> On 16 Jul 2003, at 17:26, jbrown105 at speedymail.org wrote:
> 
> 
>> I wonder how many ppl will balk at the explanation given below ;]
>> jbrown
>> 
>> On Wed, Jul 16, 2003 at 04:04:08PM -0500, C. K. Lester wrote:
> 
>> > 
>> > I don't get it. Why do some languages use 0-based indexing? It's got to be
>> > the
>> > dumbest thing in programming language history. Or maybe not.
>> > 
> 
>> Its because of the fact that (*cough* normal) computers count starting at
>> zero.
>> 
>> It is also related to the way C does things ... for an array void_pointer,
>> void_pointer[i] is the same as void_pointer+(sizeof(*void_pointer)*i)...
>> to be a bit clearer, void_pointer[i] would be the same as taking the number
>> of
>> bytes that one element of void_pointer would take up, and then multipling
>> that
>> by i, which would give the number of bytes that i elements would take up
>> (this
>> number is needed to determine where the element is located relative to the
>> start
>> of the array).
>> 
>> So, if void_pointer is an array of int's, i is 5, and sizeof(int) is 4, then
>> the
>> 6th element (remember, we start counting at zero here) is sizeof(int)*i or
>> 4*5
>> or 20 bytes away from the begining of the array.
>> 
>> The final step is to add the value held in void_pointer to what we got above,
>> this gives us an absolute memory address which we can then access like a
>> normal
>> variable. (Remember that in C an array is merely a constant pointer.)
>> 
>> Using this scheme, void_pointer[0] = void_pointer+(4*0) = void_pointer,
>> which makes the address held in void_pointer to be the very first
>> element in our array. (This is probably outdated by languages that use more
>> advanced techniques to store its data.)
>> 
>> I have heard that the technical reason that sequences in Euphoria start at
>> 1 is because in the C array that is used internally, element 0 is used to
>> hold
>> the length of the sequence. Not sure if this is true or not.
> 
> 
> BASIC and Pascal used the first byte as length. (It feels odd that RobC 
> would use an example from Basic, and still not implement CASE and 
> GOTO.) So the string storage data did actually start at zero offset, but not 
> the string itself. Naturally my gripe with Turbo Pascal is that it began a
> move
> to C strings, so one could not store a null in byte in the string. But then, 
> DOS frowned on that too.
> 
> Kat

	In which way does it frown?
	The basic display functions (int 21/09 and BIOS int 10/0E and 13) will 
happily print nulls, provided the current codepage supports them. 
Besides, for all the DOS calls I know which take an ASCIZ string as 
pointed argument, that arguent is a file, path or machine name, where 
#0-#1F are not allowed or either relevant.
	Or did I overlook anything?

CChris