Jonas Maebe schrieb:
>> If you Blockwrite a dynamic array pointer to file (i.e. because it is part of a large record) and read it back later with Blockread then the pointer value is invalid of course. BUT, if you now try to set it to nil as in
>> DynArray := nil;
>> then Free Pascal seems to free the memory where the pointer points to!
> That is in fact more or less documented: http://www.freepascal.org/docs-html/ref/refsu15.html#x39-450003.3.1 > "As remarked earlier, dynamic arrays are reference counted: if in one of the previous examples A goes out of scope and B does not, then the array is not yet disposed of: the reference count of A (and B) is decreased with 1. As soon as the reference count reaches zero the memory, allocated for the contents of the array, is disposed of." > Setting a dynamic array pointer to nil also decreases the reference count, since it removes a reference to the array data.

I would never expect an assignmet to nil changing anything else than just the value of the pointer. And for (all?) other pointers this expectation is valid.

>> This creates hard to find access violations later in your program. This cost me days of headache because never in my life I would have expected that a simple assignment with nil would do more than just setting bytes to zero. Instead of the above assignment I had to use
>> fillchar(DynArray,sizeof(DynArray),#0);
>> This solved all problems.
> It mainly creates memory leaks. If you want to keep an extra reference to a dynamic array's data, simply use another dynamic array.

No. Be aware that my dyn array pointer is part of a larger record structure which I blockwrite/-read to and from file. When I read back the structure the pointer is not valid. It's just the pointer at the time I wrote the file (could be months ago). Now I have to rebuild the stucture again. To do this I have to the pointer to nil so that following calls to SetLength have the correct assumption that no data has been allocated yet.

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