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penpenpen
Cheater
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Joined: 23 Feb 2014
Posts: 39
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 Posted: Thu Oct 09, 2014 4:02 pm Post subject: [Delphi] Crash at "SetLength(...)" |
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Hi,
I stumbled upon a problem while experimenting.
I hope we have some delphi experts here who can help  .
So Basicly what I'm doing is this:
(The Code is executed within a DLL)
Declarations:
| Code: |
var
POldCode:Pointer;
NewCode:TBytes;
OldCode:TBytes;
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| Code: |
setlength(oldcode,5);
Move(POldCode^, OldCode, sizeof(oldcode));
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... Then this code is executed
| Code: |
NewCode := CreateByteArrFromHex('C7 46 58 25 00 00 00 C7 46 54 25 00 00 00');
MeltByteArray(NewCode,OldCode);
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And in the procedure MeltByteArray it crashes when setlength is called:
| Code: |
procedure MeltByteArray(var a,b:TBytes);
var
Old: Integer;
begin
old := Length(a);
SetLength(a,old+Length(b)); //Crash
Move(b[0],a[old],Length(b)*SizeOf(b[0]));
end;
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Not Important but this is my CreateByteArrayFromHex Function:
| Code: | function CreateByteArrFromHex(ByteArr:String):TBytes;
var
i:integer;
begin
//Filter Leerzeichen
ByteArr:=StringReplace(ByteArr,' ','',[rfReplaceAll]);
i:=1; //String beginnt bei Index1
while i < length(ByteArr) do
begin
SetLength(Result,high(Result)+2);
Result[high(Result)] := HexToInt(Copy(ByteArr,i,2));
i:=i+2;
end;
end; |
I think it may have something to do with the Move Function which changes some references. But I'm not sure.
Hope you can help me |
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Dark Byte
Site Admin
 Reputation: 470
Joined: 09 May 2003
Posts: 25788
Location: The netherlands
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| Posted: Thu Oct 09, 2014 4:29 pm Post subject: |
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| Code: |
setlength(oldcode,5);
Move(POldCode^, OldCode, sizeof(oldcode));
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you're never setting POldCode to @oldcode[0] after the setlength (setlength changes the location of the array) , so POldCode will be pointing to some random memory location(worst case scenario it points to the old array that has a length of 0). Causing the move to most likely overwrite random memory in the stack. (basically, anything weird can happen from this point)
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penpenpen
Cheater
![]() Reputation: 0
Joined: 23 Feb 2014
Posts: 39
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| Posted: Thu Oct 09, 2014 4:37 pm Post subject: |
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//Edit:
I got it working .
It was a problem with the move proc. I just replaced it by CopyMemory. And it works. I still dont really understand why though. But I will find out
Thanks DarkByte |
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