Why I always get the -1 as the return of SHMessageBoxCheck function? Is there somewhere explain this issue? I have found the reason on the MSDN website, but there is no infomration for that why it return -1 as result.

Here is the code I used:

function MessageBoxCheck(hWnd: THandle; Text: PChar; Title: PChar;
dwType: DWORD; Default: Integer; RegVal: PChar): Integer;
type
TSHMessageBoxCheck = function(hWnd: THandle; Text: PChar; Title: PChar;
dwType: DWORD; Default: Integer; RegVal: PChar): Integer; stdcall;
var
hLib: THandle;
SHMessageboxCheck: TSHMessageBoxCheck;
begin
hLib := LoadLibrary('shlwapi.dll');
if hLib <> 0 then
begin
@SHMessageboxCheck := GetProcAddress(hLib, PChar(185));
if Assigned(SHMessageboxCheck) then
begin
result := SHMessageboxCheck(hWnd, Text, Title, dwType, 0, RegVal);
end
else
result := GetLastError;
end
else
result := GetLastError;
FreeLibrary(hLib);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(IntToStr(MessageBoxCheck(Handle,
PAnsiChar('Do you want to exit without saving?'#0),
PAnsiChar('Warning'#0), MB_YESNO or MB_ICONQUESTION, IDNO,
PAnsiChar('{575191FE-2069-4713-98F4-E20D1FF5BCF5}'#0))));
end;