Several methods and routines of C + + timing

1. Use the clock () function

Header file:

Clock () function that returns "the number of timer units (clock tick) for the CPU clock from the start of the program to the call to this function"

Every 1ms, Count value +1

Precision: 1 ms

#include

#include

int main ()

{

clock_t Start,end; typedef long CLOCK_T

start = Clock ();

Long i= 1000000000l;while (i--) {}

end = Clock ();

#define CLOCKS_PER_SEC ((clock_t) 1000)

Double duration = (double) (End-start)/clocks_per_sec;

printf ("%f\n", duration); 4.015

return 0;

}

2. Use the time () function

Header file:

Clock () returns the number of seconds that have elapsed since the year 1970.01.01 0:0:0 seconds.

Calendar Time

Accuracy: 1 seconds

#include

int main ()

{

time_t start,end; typedef long time_t;

Start = time (NULL); Equivalent to time (&start);

Long I=1000000000l;while (i--) {}

End = Time (NULL);

Long duration =end-start;

printf ("%ld\n", duration); 4

return 0;

}

3. Use the GetTickCount () function

Header file:

In the case of high precision, you can take advantage of the GetTickCount () function, which returns a DWORD that represents the time interval (maximum 49.7 days) experienced by the computer after startup in Ms. In a shorter timing of the timing error of 15ms, in a longer time, the timing error is low, if the timing is too long, as if the crash, CPU occupancy rate is very high, can only be used for the delay of the program is not high.

Accuracy: 1 ms, short time error 15ms

#include

#include

int main ()

{

DWORD Start,end;//typedef unsigned long DWORD;

Start = GetTickCount ();

Long I=1000000000l;while (i--) {}

End = GetTickCount ();

Double duration = (double) (End-start)/1000;

printf ("%f\n", duration); 3.922

return 0;

}

4. Use the Queryfrequencycount () function

Header file:

High Precision Counters

Accuracy: 1 microseconds, error no more than 0.5 subtle (precision is 1000 000/(CPU frequency) microseconds)

#include

#include

int main ()

{

Large_integer F;

QueryPerformanceFrequency (&f)//Get internal high-precision counter frequency

Double dfreq;

Dfreq = (double) F.quadpart; Get the frequency of the counter

Large_integer Start,end;

QueryPerformanceCounter (&start); Gets the current count value of the internal high-precision counter

Long I=1000000000l;while (i--) {}

QueryPerformanceCounter (&end);

Time difference = count value/frequency (unit s)

Double duration = (double) (end. Quadpart-start.quadpart)/dfreq;

printf ("%f\n", duration);//3.969499

return 0;

}