(* --------- Sample (GetSystemDirectory) --------- *)

var
     parameters: array of Pointer;
     returned: Cardinal;
     Dir: String;
begin
     SetLength(parameters, 2);
     SetLength(Dir, MAX_PATH); // Set Buffer size
     parameters[0] := Pointer(@Dir[1]); // 1st parameter, buffer for path string
     parameters[1] := Pointer(MAX_PATH); // 2nd parameter, length of buffer
     if not DynamicDllCallName(kernel32, 'GetSystemDirectoryA', true, returned, parameters) then begin
       ShowMessage('Function could not be found!');
     end else begin
       SetLength(Dir, returned); // Cut String
       ShowMessage('GetSystemDirectoryA:'#13#10'Path: ' + Dir + #13#10'Length: ' + IntToStr(returned));
     end;
end;

(* --------- Sample (TextOut) --------- *)

const
     SampleText = 'test';
var
     parameters: array of Pointer;
     returned: Cardinal;
begin
     SetLength(parameters, 5);
     parameters[0] := Pointer(Canvas.Handle); // 1st parameter, handle to the form's canvas
     parameters[1] := Pointer(10); // 2nd parameter, left margin
     parameters[2] := Pointer(30); // 3rd parameter, top margin
     parameters[3] := @SampleText[1]; // 4th parameter, pointer to the sample string
     parameters[4] := Pointer(Length(SampleText)); // 5th parameter, length of the sample string
     if not DynamicDllCallName(gdi32, 'TextOutA', true, returned, parameters) then begin
       ShowMessage('Function could not be found!');
     end else begin
       if not BOOL(returned) then begin // function's result = false
         ShowMessage('TextOut() failed!');
       end;
     end;
end;

(* --------- Sample (LockWorkStation) --------- *)

var
     parameters: array of Pointer;
     returned: Cardinal;
begin
     // We don't have parameters, so we don't touch parameters
     if not DynamicDllCallName(user32, 'LockWorkStation', true, returned, parameters) then begin
       ShowMessage('Function could not be found!');
     end else begin
       if not BOOL(returned) then begin
         ShowMessage('LockWorkStation() failed!');
       end;
     end;
end;