[fpc-pascal] Array clearing

Sven Barth pascaldragon at googlemail.com
Thu Apr 13 14:26:20 CEST 2017

Am 13.04.2017 13:25 schrieb "MARCOU Gilles" <g.marcou at unistra.fr>:
> Regarding this code:
>> SetLength(Array,Length(Array)+1);
>> Array[High(Array)] := …
> as I understood from (http://wiki.freepascal.org/Dynamic_array),
SetLength will create a copy of the array and free the memory of the
shorter array. In this case, a lot of memory operations and copy operations
are performed thus degrading the performances of the code. Then it would be
unwise to use such strategy: better allocate the size of the array
correctly at the beginning of the run, or resize the array by block, to
decrease the frequency of such operation:
>> SetLength(Array,Length(Array)+N);
> Can somebody confirm (or invalidate) this?

SetLength() uses reallocation for the memory. So it *might* work without
copying though that is not guaranteed.
But in general it's recommended anyway not to do "SetLength(..., ... + 1)"
loops as that will lead to fragmentation of the heap.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freepascal.org/pipermail/fpc-pascal/attachments/20170413/45718383/attachment.html>

More information about the fpc-pascal mailing list