Valient's IT Notes: 2012

The obvious solution to the problem how to disable overflow checks in Delphi:

{$OVERFLOWCHECKS OFF}
// code here
{$OVERFLOWCHECKS ON}

Such a snippet will automatically cause the overflow-checking to suddenly become enabled after running regardless of what it was before, even if it wasn't previously enabled in compiler options or code.
{$Q+} is brief notation for {$OVERFLOWCHECKS ON} and {$Q-} is notation for {$OVERFLOWCHECKS OFF} respectively.
Prefer to resort to this crutch construction which does not change the check state in the rest of the project:

{$IFOPT Q+}
  {$DEFINE OVERFLOW_ON}
  {$Q-}
{$ELSE}
  {$UNDEF OVERFLOW_ON}
{$ENDIF}
//
// Your code here
// 
{$IFDEF OVERFLOW_ON}
  {$Q+}
  {$UNDEF OVERFLOW_ON}
{$ENDIF}

Disabling overflow checks in Delphi