function

clock

<ctime>
clock_t clock ( void );
Clock program
Returns the processor time consumed by the program.

The value returned in expressed in processor clock ticks. The macro constant CLOCKS_PER_SEC specifies the relation between a clock tick and a second (clock ticks per second).

The epoch used as reference by clock may vary between platforms, but it is related to the program execution (generally its launch). To calculate the actual processing time of a program, the value returned by clock should be compared to a value returned by a previous call to the same function.

Parameters

(none)

Return Value

The number of clock ticks elapsed since an epoch related to the particular program execution.

On failure, the function returns a value of -1.

clock_t is a type defined in <ctime> to some type capable of representing clock tick counts and support arithmetical operations (generally a long integer).

Example

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/* clock example: frequency of primes */
#include <stdio.h>
#include <time.h>
#include <math.h>

int frequency_of_primes (int n) {
  int i,j;
  int freq=n-1;
  for (i=2; i<=n; ++i) for (j=sqrt(i);j>1;--j) if (i%j==0) {--freq; break;}
  return freq;
}

int main ()
{
  clock_t t;
  int f;
  t = clock();
  printf ("Calculating...\n");
  f = frequency_of_primes (99999);
  printf ("The number of primes lower than 100,000 is: %d\n",f);
  t = clock() - t;
  printf ("It took me %d clicks (%f seconds).\n",t,((float)t)/CLOCKS_PER_SEC);
  return 0;
}


Output:

Calculating...
The number of primes lower than 100,000 is: 9592
It took me 143 clicks (0.143000 seconds).

See also