On 01 Apr 2011, at 18:44, Jürgen Hestermann wrote: > 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.
That expectation is not valid for any reference counted type (be it a dynamic array, ansistring, unicodestring, COM-style interfaces). That's the whole point of reference counted types: they keep track of how many references still exist to the data, and once that reaches zero the data is freed. > 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. The correct way to do so is to call initialize() on the field. Jonas_______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
