---
name: "QwtSystemClock"
section: "3"
platform: "linux"
package: "libqwt-doc"
version: "6.1.4-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/QwtSystemClock"
---

# QwtSystemClock(3)

QwtSystemClock provides high resolution clock time functions.

## NAME

QwtSystemClock - **QwtSystemClock** provides high resolution clock time functions.

## SYNOPSIS

`#include <qwt_system_clock.h>`

### Public Member Functions

**QwtSystemClock** ()\
 Constructs a null clock object.  virtual **~QwtSystemClock** ()\
 Destructor.  bool **isNull** () const\
 void **start** ()\
 double **restart** ()\
 double **elapsed** () const\

## Detailed Description

**QwtSystemClock** provides high resolution clock time functions.

Sometimes the resolution offered by QTime ( millisecond ) is not accurate enough for implementing time measurements ( f.e. sampling ). **QwtSystemClock** offers a subset of the QTime functionality using higher resolution timers ( if possible ).

Precision and time intervals are multiples of milliseconds (ms).

( **QwtSystemClock** is obsolete since Qt 4.8 as QElapsedTimer offers the same precision )

**Note:**

The implementation uses high-resolution performance counter on Windows, mach\_absolute\_time() on the Mac or POSIX timers on other systems. If none is available it falls back on QTimer.

## Member Function Documentation

### double QwtSystemClock::elapsed () const

**Returns:**

Number of milliseconds that have elapsed since the last time **start()** or **restart()** was called or 0.0 for null clocks.

### bool QwtSystemClock::isNull () const

**Returns:**

true if the clock has never been started.

### double QwtSystemClock::restart ()

Set the start time to the current time

**Returns:**

Time, that is elapsed since the previous start time.

### void QwtSystemClock::start ()

Sets the start time to the current time.

## Author

Generated automatically by Doxygen for Qwt User's Guide from the source code.