Read REG_BINARY to String - winapi

Question

I use this code to read binary data from the registry to a string
function ReadBinary (RootKey: HKEY; SubKey,ValueName: WideString; var Data : String): Bool;
var
Key : HKey;
Buffer : array of char;
Size : Cardinal;
RegType : DWORD;
begin
result := FALSE;
RegType := REG_BINARY;
if RegOpenKeyExW(RootKey, pwidechar(SubKey), 0, KEY_READ, Key) = ERROR_SUCCESS then begin
if RegQueryValueExW(Key,pwidechar(ValueName),NIL,#RegType, NIL,#Size) = ERROR_SUCCESS then begin
SetLength (Buffer, Size + 1);
FillChar(Buffer, SizeOf (Buffer), #0);
if RegQueryValueExW(Key,pwidechar(ValueName),NIL,#RegType, #Buffer[0],#Size) = ERROR_SUCCESS then begin
result := TRUE;
Data := String (Buffer); // Shows empty or sometimes 1 random char.
end;
end;
end;
RegCloseKey (Key);
end;
EDIT2:
It works fine with a fixed declared array of byte/char
function ReadBinary (RootKey: HKEY; SubKey,ValueName: WideString; var Data : String): Bool;
var
Key : HKey;
Buffer : array [0..200] of char;
Size : Cardinal;
RegType : DWORD;
begin
result := FALSE;
RegType := REG_BINARY;
if RegOpenKeyExW(RootKey, pwidechar(SubKey), 0, KEY_READ, Key) = ERROR_SUCCESS then begin
if RegQueryValueExW(Key,pwidechar(ValueName),NIL,#RegType, NIL,#Size) = ERROR_SUCCESS then begin
FillChar(Buffer, SizeOf (Buffer), #0);
if RegQueryValueExW(Key,pwidechar(ValueName),NIL,#RegType, #Buffer,#Size) = ERROR_SUCCESS then begin
result := TRUE;
Data := String (Buffer);
end;
end;
end;
RegCloseKey (Key);
end;
I'm stuck.
What do I do wrong and what is the solution?
Thank you for your help.
EDIT:
I am aware of that I am reading binary data from the registry. So it might be already 0 terminated and can return false results. I can guarantee that there are no #0 chars in the binary data because I wrote a long text (String with CR/LF) in the Value before.

Answer 1

Buffer: array of char;
is dynamic array of chars, that is, in fact, pointer variable. And this string resets the pointer to Nil:
FillChar(Buffer, SizeOf (Buffer), #0);
So dynamic array is not valid now.
To fill the contents of dynamic array by zeroes, you have to use
FillChar(Buffer[0], SizeOf(Buffer[0]) * Length(Buffer), #0)
but this is not necessary, because SetLength makes the job.

Answer 2

dynamic array is somethign like pointer. In C/C++ it would be exactly the same. In Delphi it is not, but you may for semantics think this way. #Buffer is not address of 1st car, but the address of the pointer itself. Ib both calls to FillChar and RegQueryValueExW you should pass Buffer[0] and #Buffer[0] instead
Why do u use Windows API instead of standard TRegistry ? Or maybe TNT Unicode Controls or somethign similar have readymade unicode-aware registry access.
Win API xxxxxxxW functions are unicode aware. Did you checked what data you got ? Is it 8-but or 16-bit ? look received data as array of bytes in HEX - do they contain $00 bytes or not ? It looks like they do and you got unicode data into the buffer. Then it would be expected and correct behaviour of string to only accept 1 letter (or 0, depending on intel or motorola byte order). Check what binary data you've got in Buffer.
Personally, i'd made Buffer as array of bytes. Then after registry access i'd used SetString procedure to get value if D7 has it. If not, then i'd copy it like SetLength(Data, Size); Move(Buffer[0], Data[1], Size); And i'd remove FillChar completely. This way copying would be both slightly faster and not break on 1st stray #0 byte.
I'd not use ambiguous char and string types when doing low-level binary data typecasting, but rather use concrete AnsiString and AnsiChar types. If your code would somewhen be compiled by newer Unicode-capable Delphi or FreePascal, that would keep it working. Shortcuts "char" and "string" may change their meaning depending on compiler version. And then you would have hard time determining why and where it broke and what to do.