On 01 Apr 2011, at 18:04, Jürgen Hestermann wrote: > 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. > 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. Jonas_______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
