[fpc-pascal] Array clearing

Sven Barth pascaldragon at googlemail.com
Tue Apr 4 17:12:32 CEST 2017

On 04.04.2017 16:27, Ryan Joseph wrote:
>>> Does SetLength on a single level dynamic array not even allocate a continuous block of memory?
>> Yes, it does (as explained in all the other mails).
>> A (dynamic) array of integer will be allocated as a single block by SetLength.
>> So if you only have one level of a dynamic array as in
>> var MyArray : array of integer;
>> then SetLength(MyArray,1000) will allocate a single block of 1000 integers.
>> But with
>> var MyArray : array of array of integer;
>> SetLength(MyArray,1000);
>> will allocate a single block of 1000 pointers (to an array of integer each).
>> Then, SetLength(MyArray[0],1000) will allocate one (!) block of 1000 integers.
>> SetLength(MyArray[1],1000) will allocate another block of 1000 integers and so on….
> I was allocating using SetLength(MyArray, 3, 3, 3) for a 3x3x3 matrix for example. Maybe it depends on the memory manager and the state of heap but if you called early in the programs execution it should be allocate all that memory in one block I would think. 

Addendum: If you look at fpc_dynarray_setlength() again then you'll see
at line 289 that it's calling itself recursively for nested arrays.


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