# QwtSystemClock Class Reference

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

`#include <qwt_system_clock.h>`

List of all members.

## Public Member Functions

double | elapsed () const
bool | isNull () const
| QwtSystemClock ()
double | restart ()
void | start ()
virtual | ~QwtSystemClock ()

## Static Public Member Functions

static double | precision ()

## 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).

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.

## Constructor & Destructor Documentation

QwtSystemClock::QwtSystemClock | ( |  | ) |

Constructs a null clock object.

QwtSystemClock::~QwtSystemClock | ( |  | ) | `[virtual]`

Destructor.

## 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::precision | ( |  | ) | `[static]`

Returns:
  Accuracy of the system clock in milliseconds.

double QwtSystemClock::restart | ( |  | ) |

The start time to the current time and return the time, that is elapsed since the previous start time.

void QwtSystemClock::start | ( |  | ) |

Sets the start time to the current time.