[fpc-pascal] about dynamic array
jonas.maebe at elis.ugent.be
Thu May 6 12:00:21 CEST 2010
On 06 May 2010, at 11:39, spir ☣ wrote:
> Where can one find information on types like dynamic array? Also, on
> funcs or procs that apply on them, like setLength & copy.
In the documentation: http://www.freepascal.org/docs-html/ref/refsu14.html
> * Can one rely on the fact that setLength keeps existing data (in
> the range of the new size), both when up- and down-sizing?
> * How is resizing actually performed (is the data moved to a newly
> allocated area)?
> * Does copy onto a dynamic array automatically resize (setLength),
> even if the target is greater than needed? (I would like no.)
Copy() creates a copy of the original dynamic array. If you assign the
result afterwards to another dynamic array, that other dynamic array
is finalised. The copy() operation itself has no idea about what you
will do with the result.
> * Can one set the first index where to copy on the target array? (eg
> to join 2 arrays into a greater one, or to extend an existing one
> that has free space at tail)
> * Can one use copy from/to a *static* array? (If no, why not?)
No, simply because copy() is only defined for dynamic arrays.
> * What other differences with static array, if any? (Aside the fact
> that one does not need to explicitely reallocate and copy on
Please read the monster thread that I just closed, rather than
starting it all over again.
> For Christmas:
> * Can one add or remove an element --at the end? (And have the array
> behave accordingly.)
Use setlength to increase/decrease the length by one and add/
> * Can one add or remove an element --anywhere? (And have the array
> behave accordingly.)
Not trivially/efficiently. In general, if you want to do something
like that you should use a linked list rather than an array. Arrays
are notoriously inefficient (even if you use plain static arrays with
move() and other low level operations) if you often have to insert/
delete elements in the middle.
> If the answers to last 2 questions is "only every 29th of februar",
> how can one have a "flexible" array? Is there something like that in
> stock? Would you implement it on top of dynamic array, or rather
> from scratch on top of static array (since the "dynamicity" does not
> seem very helpful)?
Don't use a hammer to tighten screws.
More information about the fpc-pascal