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From: jmatthews@desire.wright.edu
Newsgroups: comp.sys.mac.programmer
Subject: Re: Variable length arrays in Pascal--can it be done?
Message-ID: <1991Apr4.124257.3095@desire.wright.edu>
Date: 4 Apr 91 17:42:57 GMT
References: <1521@babcock.cerc.wvu.wvnet.edu>
Organization: University Computing Services, Wright State University
Lines: 47

In article <1521@babcock.cerc.wvu.wvnet.edu>, vrm@blackwater.cerc.wvu.wvnet.edu (Vasile R. Montan) writes:
> I want to have variable length arrays in Pascal.  Pascal, however,
> does not want me to have variable length arrays in it.  I think I've
> figured out a way to do this.
> ...
> Suppose I define a type in Pascal which is an arbitrarily large
> array: say, one with 10000 elements in it, or some number larger than
> I will ever need.  Suppose I then define a pointer to point to
> this type, and a handle to point to the pointer.  Let's say I want
> to start out with seven elements in the array, so I use NewHandle
> and allocate just enough memory to hold those seven elements.  I
> store this number seven in a variable to keep track of how big
> the array is.
> 
> Now, as long as I am careful not to refer to any elements beyond the
> end of the memory block, I should not have any problems, right?
> And if I want to resize the array, I can use SetHandleSize,
> making sure to keep track of how many elements are now in the array,
> right?  Is there any reason why this shouldn't work?
> 
> --Kurisuto
> un020070@vaxa.wvnet.edu

Your technique is sound. I think that's how TextEdit's lineStarts array and
the List Manager's cellArray work. Notice that only the lower array bound
matters: it determines whether the array starts with element 0 or 1. The
upper bound is immaterial since you'll never create an instance variable
of this type, only a pointer to it.

Moreover, you can keep the count with the array
	Type MyArray = record
			count:Integer;
			elements: array[1..1] of MyArrayElemnt
			end;

Finally, I recently "discovered" the ToolBox Utility PtrAndHand. It's great
in this context since it does the GetHandleSize, SetHandleSize and
BlockMove stuff you'ld have to do yourself. You can always get a Ptr to
the source data with the @ operator and the destination handle can be unlocked
(PtrAndHand does the right thing internally, I think:-).

Hope this helps, John

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| John B. Matthews, jmatthews@desire.wright.edu, am103@cleveland.freenet.edu |
| "Say...what's a mountain goat doing way up here in a cloud bank?" - Larson |
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