On Wed, 30 Aug 2017, Bo Berglund via Lazarus wrote:
I just want to check with you which way is safer when using Move() commands in a procedure to combine two TBytes arrays by inserting one into the other at a specified point. What I need to do is the following: - Increase the size of the Dest array by the length of the Src array - Move the data following the insertion point in the Dest array towards the end starting at Index - Copy the data from the Src array into Dest at Index where the hole has been created Like this: procedure InsertBytes(var Dest: TBytes; Src: TBytes; Index: integer); var LenD, LenS: integer; begin if Length(Src) = 0 then exit; LenD := Length(Dest); LenS := Length(Src); if Index > LenD then Index := LenD; //Make an append instead SetLength(Dest, LenD + LenS); Move(Dest[Index], Dest[Index + LenS], LenD - Index); //Create space Move(Src[0], Dest[Index], LenS); //Insert data end; If the calculation of the number of bytes to move (LenD - Index) for some reason is wrong and results in too many bytes being moved, what will happen then? Will Move() overwrite whatever is following the Dest array in memory?
Yes.
Would it be safer to use a local intermediate array to combine Dest and Src and then in the end Move the data back into Dest?
Not really. If you calculate lengths wrong, the end result is unpredictable in any case.
I have tested the above procedure and it looks OK, but I am worried that in some cases the same kind of construct would be wrong and maybe cause unknown side effects. I must use Move() for handling other data of various kinds like packed records and such too...
If the packed records contain managed data (ansistrings and the like): Don't use move.
Michael. -- _______________________________________________ Lazarus mailing list Lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
