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Class Library Reference Manual


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Chapter 8
Stopwatch Package

The Stopwatch package provides ways to measure intervals of program execution time. The package consists of a single class, Stopwatch . Typically, you use this class during the performance-tuning phase of program development.


Stopwatch class

Provides the means to measure intervals of time between specified program events.

Header

#include <stopwatch.hxx>

Alternative Header

#include <Stopwatch.h>


Declaration


class Stopwatch 
{ 
public: 
                     Stopwatch(); 
 
   void              start(); 
   void              stop(); 
   void              reset(); 
   int               status() const; 
   double            system() const; 
   double            user() const; 
   double            real() const; 
 
   static double     resolution(); 
};               

Description

Objects of this class measure program execution time and return the result in floating-point seconds. The class includes the start , stop , and reset functions familiar to users of a mechanical stopwatch.

You can time the entire program or select certain portions of the program to time; for example, a specified loop or program module. You can create a different Stopwatch object for each independent program activity, and name each according to the activity you intend to measure.


Constructor

Stopwatch()

Constructs a Stopwatch object with both time and running status initialized to 0.

Member Functions

double real() const

Returns real time (clock time) in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

void reset()

Resets the current time measurement to 0 without affecting the value of status() . If status() is initially nonzero, time measurement continues uninterrupted after resetting.

double resolution()

Returns the (system dependent) resolution of measured time in double-precision, floating-point seconds.

void start()

Begins measuring program execution time when status() is initially 0 ( status() becomes nonzero as a consequence of the call). If status() is initially nonzero, the call has no effect.

int status() const

Indicates whether the stopwatch is running (returns a value of 1) or not running (returns a value of 0).

void stop()

Halts measurement of program execution time when status() is initially nonzero ( status() becomes 0 as a consequence of the call). If status() is initially 0, the call has no effect.

double system() const

Returns the system CPU time in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

double user() const

Returns the user CPU time in double-precision, floating-point seconds. You can call this function while the stopwatch is running.

System Environment

A typical value for the resolution of execution time is 1/60 second.

Example


Stopwatch w ; 
w.start() ; 
//...
// some computation you want to time goes here 
//...
w.stop() ; 
cout << "elapsed time was " << w.user() << "\n"; 
      

Displays the number of seconds the computation takes to run. The result is a double-precision value.


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