LastOSError (Delphi)

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Description

This code demonstrates the use of system error codes and how to transform them into Delphi exceptions.

Code

procedure TForm2.btRaiseLastClick(Sender: TObject);
begin
  { Set the last OS error to a bogus value. }
  System.SetLastError(ERROR_ACCESS_DENIED);

  try
    RaiseLastOSError();
  except
    on Ex : EOSError do
      MessageDlg('Caught an OS error with code: ' + IntToStr(Ex.ErrorCode), mtError, [mbOK], 0);
  end;

  { Let the Delphi Exception dialog appear. }
  RaiseLastOSError(ERROR_NOT_ENOUGH_MEMORY);

  { Finally set the last error to none. }
  System.SetLastError(ERROR_SUCCESS);

  if GetLastError() <> ERROR_SUCCESS then
    MessageDlg('Whoops, something went wrong in the mean time!', mtError, [mbOK], 0);

  { No exception should be thrown here because last OS error is "ERROR_SUCCESS". }
  CheckOSError(GetLastError());
end;

Uses

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