I believe it is a compiler error and will raise a QA ticket Thanks for your help
D On 26/08/11 08:17, Peter Ingham wrote: > Try filling LogData with binary zeros after the Getmem& before the assign. > > FillChar (LogData^, sizeof(TLogData), 0); > > I believe the uninitialized memory is messing up the compiler magic > associated with the dynamic array. > > > Any reason the local Tlogdata record is referenced via a pointer? > > I suspect the following will also work: > procedure TUserClass.Log(const LogType: TLogType; const Args: array of > const ); > var > LogData: TLogData; > begin > LogData.LogType := LogType; > LogData.LogArgs := CreateConstArray(Args); > // ... do some other stuff with the LogData item finally calling > end; > > Cheers > > On 26/08/2011 1:49 a.m., David Moorhouse wrote: >> Hi Peter >> >> Been there done that :) >> >> The function call is fine. It is the assignment that causes the AV - >> because the "bucket" is too small. >> Assigning it with 16 bytes fixes the problem, regardless of how many >> items the array holds. >> >> I smell compiler magic in the background. >> >> Cheers > >> D >> >> On 25/08/11 17:29, Peter Ingham wrote: >>> Another attempt to reply... >>> >>> First thing to do is determine if the crash occurs in the procedure call, >>> on the subsequent assign, or in between. >>> >>> Give this a try: >>> procedure TUserClass.Log(const LogType: TLogType; const Args: array of >>> const ); >>> var >>> LogData: PLogData; >>> TempArgs : TConstArray; >>> begin >>> // size of record TLogData does not work >>> GetMem(LogData, sizeof(TLogData)); >>> LogData.LogType := LogType; >>> // blows up on one of these lines >>> TempArgs := CreateConstArray(Args); >>> LogData.LogArgs := TempArgs; >>> // ... do some other stuff with the LogData item finally calling >>> FreeMem >>> end; >>> >>> >>> Regarding the size of a dynamic array, like a string variable, the >>> variable (LogArgs in this case) is the size of a pointer (i.e. 4 bytes >>> for Win32). If the pointer is non-zero, it points to a structure which >>> includes the adjacent array elements preceded by a length. >>> >>> One thing to watch out for is that Getmem does not clear the allocated >>> memory, so LogData after the Getmem call will contain any old rubbish. >>> The reference to LogData.LogArgs in the assignment may be >>> dereferencing a non-zero pointer& attempting to use whatever it >>> contains. >>> >>> Cheers >>> >>> >>> On 25/08/2011 11:40 a.m., David Moorhouse (DUG) wrote: >>>> I have the following code snippet >>>> >>>> <code> >>>> type >>>> PConstArray = ^TConstArray; >>>> TConstArray = array of TVarRec; >>>> >>>> function CreateConstArray(const Elements: array of const): TConstArray; >>>> >>>> type >>>> TLogType = (ltError, ltWarn, ltInfo); >>>> PLogData = ^TLogData; >>>> TLogData = record >>>> LogType: TLogType; >>>> LogArgs: TConstArray; >>>> end; >>>> >>>> .... >>>> >>>> procedure TUserClass.Log(const LogType: TLogType; const Args: array of >>>> const ); >>>> var >>>> LogData: PLogData; >>>> begin >>>> // size of record TLogData does not work >>>> GetMem(LogData, sizeof(TLogData)); >>>> LogData.LogType := LogType; >>>> // blows up on next line >>>> LogData.LogArgs := CreateConstArray(Args); >>>> // ... do some other stuff with the LogData item finally calling >>>> FreeMem >>>> end; >>>> >>>> function CreateConstArray(const Elements: array of const): TConstArray; >>>> var >>>> I: Integer; >>>> begin >>>> SetLength(Result, Length(Elements)); >>>> for I := Low(Elements) to High(Elements) do >>>> Result[I] := // assign a TVarRec here >>>> end; >>>> </code> >>>> >>>> The code that assigns the memory only assigns 8 bytes - and an access >>>> violation ensues. If I replace the call to "sizeof" with the number 16, >>>> the code works fine. >>>> >>>> My understanding of dynamic arrays was that the compiler created a 4 >>>> byte >>>> field before the first element that contained the length of the array. >>>> >>>> So why does the sizeof function not reflect this ? And why do I >>>> need 16 >>>> bytes not 12 (4 for LogType + 4 for length of array + 4 for array >>>> pointer)? >>>> Also regardless of the number of items in the open array parameter, 16 >>>> bytes works, so it does not relate the length of the TConstArray. >>>> >>>> Your thoughts ? >>>> >>>> David >>>> >>>> >>>> >>>> _______________________________________________ >>>> NZ Borland Developers Group - Delphi mailing list >>>> Post: delphi@delphi.org.nz >>>> Admin: http://delphi.org.nz/mailman/listinfo/delphi >>>> Unsubscribe: send an email to delphi-requ...@delphi.org.nz with >>>> Subject: unsubscribe >>>> >> >> _______________________________________________ >> NZ Borland Developers Group - Delphi mailing list >> Post: delphi@delphi.org.nz >> Admin: http://delphi.org.nz/mailman/listinfo/delphi >> Unsubscribe: send an email to delphi-requ...@delphi.org.nz with Subject: >> unsubscribe >> > _______________________________________________ > NZ Borland Developers Group - Delphi mailing list > Post: delphi@delphi.org.nz > Admin: http://delphi.org.nz/mailman/listinfo/delphi > Unsubscribe: send an email to delphi-requ...@delphi.org.nz with Subject: > unsubscribe _______________________________________________ NZ Borland Developers Group - Delphi mailing list Post: delphi@delphi.org.nz Admin: http://delphi.org.nz/mailman/listinfo/delphi Unsubscribe: send an email to delphi-requ...@delphi.org.nz with Subject: unsubscribe
