Time intervals measurement

Using Windows API GetTickCount

The Windows API GetTickCount function returns the number of milliseconds since the system (computer) was started. The simplest example follows:

var
  Start, Stop, ElapsedMilliseconds: cardinal;
begin
  Start := GetTickCount;
  // do something that requires measurement
  Stop := GetTickCount;
  ElapsedMillseconds := Stop - Start;
end;

Note that GetTickCount returns 32-bit DWORD so it wraps every 49.7 days. To avoid wrapping, you may either use GetTickCount64 (available since Windows Vista) or special routines to calculate tick difference:

function TickDiff(StartTick, EndTick: DWORD): DWORD;
begin
  if EndTick >= StartTick
    then Result := EndTick - StartTick
    else Result := High(NativeUInt) - StartTick + EndTick;
end;

function TicksSince(Tick: DWORD): DWORD;
begin
  Result := TickDiff(Tick, GetTickCount);
end;

Anyway these routines will return incorrect results if the interval of two subsequent calls of GetTickCount exceeds the 49.7 day boundary.

To convert milliseconds to seconds example:

var
  Start, Stop, ElapsedMilliseconds: cardinal;
begin
  Start := GetTickCount;
  sleep(4000); // sleep for 4 seconds
  Stop := GetTickCount;
  ElapsedMillseconds := Stop - Start;
  ShowMessage('Total Seconds: '
      +IntToStr(round(ElapsedMilliseconds/SysUtils.MSecsPerSec))); // 4 seconds
end;

Using TStopwatch record

Recent versions of Delphi ships with the TStopwatch record which is for time interval measurement. Example usage:

uses
  System.Diagnostics;

var
  StopWatch: TStopwatch;
  ElapsedMillseconds: Int64;
begin
  StopWatch := TStopwatch.StartNew;
  // do something that requires measurement
  ElapsedMillseconds := StopWatch.ElapsedMilliseconds;
end;