Re: Stack vs. heap?

[Don Bruder <dakidd@sonic.net>]

In article <W9cmg.37$oA2.73@news.oracle.com>,
 Martin Doherty <martin.doherty@undisclosed.com> wrote:

> I believe I thoroughly understand the operation of a stack, but the term 
> "heap" is a mystery.  I know it's used in UCSD/Apple Pascal for memory 
> management functions of some kind; can anyone explain to me what a heap 
> is in general concept, and what it's used for in Pascal?
> 
> Thanks
> Martin

Stack: 
A segment of memory where fixed-size values (typically one logical 
"word" in size, regardless of whether the word is 1 byte, 2 bytes, 4 
bytes, or some other number of bytes) get "pushed" and "popped" for 
temporary storage - The first value pushed is the last to be popped. See 
also "last in, first out" (AKA "LIFO") queue. Although the operation of 
a stack and a LIFO is generally handled differently at the "Step 1 do 
this, step 2 do that, step 3 do something else..." level, they perform 
in exactly the same way at the "overall picture" level.

Heap:
A segment of memory where chunks of arbitrary sizes get allocated, used 
for storage, then released for re-use. See also "memory pool". 

"Heap" can have variou meanings depending on the machine architecture 
and programming model and/or language being used. In the case of Apple 
Pascal, "Heap" generally refers to "all of the memory allocated to the 
program that isn't executable code, static strings, constant values, or 
declared variables". Arrays are generally in the heap. Likewise, the 
values of string variables (which are, of course, little more than a 
special case of arrays in Pascal)

-- 
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