Format
#include <time.h>
double difftime(time_t time2, time_t time1);Language Level: ANSI
Threadsafe: Yes.
Description
The difftime() function computes the difference in seconds between time2 and time1.
Return Value
The difftime() function returns the elapsed time in seconds from time1 to time2 as a double precision number. Type time_t is defined in <time.h>.
Example that uses difftime()
This example shows a timing application that uses difftime(). The example calculates how long, on average, it takes to find the prime numbers from 2 to 10 000.
#include <time.h>
#include <stdio.h>
#define RUNS 1000
#define SIZE 10000
int mark[SIZE];
int main(void)
{
time_t start, finish;
int i, loop, n, num;
time(&start);
/* This loop finds the prime numbers between 2 and SIZE */
for (loop = 0; loop < RUNS; ++loop)
{
for (n = 0; n < SIZE; ++n)
mark [n] = 0;
/* This loops marks all the composite numbers with -1 */
for (num = 0, n = 2; n < SIZE; ++n)
if ( ! mark[n])
{
for (i = 2 * n; i < SIZE; i += n)
mark[i] = -1;
++num;
}
}
time(&finish);
printf("Program takes an average of %f seconds "
"to find %d primes.\n",
difftime(finish,start)/RUNS, num);
}
/******************** Output should be similar: *****************
The program takes an average of 0.106000 seconds to find 1229 primes.
*/Related Information