Can Delphi only use a .dll if required?

Question

I have added these two methods to the 1st unit of my Delphi 5 application.

function Inp(PortAddress: Integer): Integer; stdcall; external 'inpout32.dll' name 'Inp32';

procedure Output(PortAddress, Value: Integer); stdcall; external 'inpout32.dll' name 'Out32';

However I don't want to have to issue the inpout32 library with the software unless they explicitly need it. Currently the program says "Not Found" upon executing unless they're present in the root or System32.

Users will only call these methods if they have a specific option set, but this is not gathered from the .ini file until after the inpout library is used.

Is there a way to only use this library when required like some components do, rather than declaring it the way I have?

Answer 1

In Delphi versions prior to 2010, you have to use classic dynamic loading. Consider this typical (and simple) example calling the Beep function from Kernel32.dll (which you should not hardcode the path to in real code, of course!):

type
  TBeepFunc = function(dwFreq: DWORD; dwDuration: DWORD): BOOL; stdcall;

procedure TForm4.FormClick(Sender: TObject);
var
  lib: HMODULE;
  prc: TBeepFunc;
begin

  lib := LoadLibrary('C:\WINDOWS\System32\Kernel32.dll');
  if lib = 0 then RaiseLastOSError;
  try
    @prc := GetProcAddress(lib, 'Beep');
    if Assigned(prc) then
      prc(400, 2000)
    else
      ShowMessage('WTF? No Beep in Kernel32.dll?!');
  finally
    FreeLibrary(lib);
  end;
end;