Re: [Lazarus] Use of Move()?

[Marc Weustink]

On 1-2-2011 23:51, Bo Berglund wrote:

On Tue, 01 Feb 2011 23:33:58 +0100, Marc Weustink
<m...@dommelstein.net>  wrote:

Just tested:

program MoveTest;
{$mode objfpc}{$H+}
uses
   SysUtils;
var
   S: String;
   I: Integer;
   P: Pointer;
begin
   S := 'Bla';
   S := S + S;
   P := @I;
   Move(S[1], P^, SizeOf(I));

   WriteLn(Format('%x %x %x %x %8.8x', [Ord(S[1]), Ord(S[2]), Ord(S[3]),
Ord(S[4]), i]));
end.

$ ./movetest
42 6C 61 42 42616C42

My code is a bit more complex because I want to be able to read and
write different types of variables to the buffer handler.
As an example I have the case of a string variable. To write it into
the buffer I use this overloaded write:

function TSSCommBuf.Write(const Source: string): boolean;
begin
   Result := Write(@Source[1], Length(Source));
end;

and for a Cardinal argument I use this:

function TSSCommBuf.Write(const Source: Cardinal): boolean;
begin
   Result := Write(@Source, SizeOf(Source));
end;

both of which then calls the main Write:

function TSSCommBuf.Write(Source: Pointer; Count: Cardinal): boolean;
var
   b: byte; //For debugging, will be removed later
   Dst: Pointer; //Suggestion from Marc Weustink
begin
   Result := false;
   //Check buffer size and grow if needed
   if (FBufSize - FWriteIndex)<  Count then
     ExpandBuffer(FWriteIndex - FBufSize + Count);
   Dst := @FBuf[FWriteIndex];
   Move(Source, Dst^, Count); // Source and Dst are pointers
   b := FBuf[FWriteIndex]; //To check what actually was written
   FWriteIndex := FWriteIndex + Count;
   Result := true;
end;

When I call the Write method with a string argument I get first to the
small overloaded function, which unifies the arguments and calls the
main Write.

But when I test this with the string containing the single char #6
then the value that actually gets written is #64....

So somehow I am missing something important here...

Move expects 2 untyped parameters, so dereference your pointers

  Move(Source^, Dst^, Count); // Source and Dst are pointers

Marc

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