Format
#include <time.h> double difftime(time_t time2, time_t time1);
Language Level: ANSI, POSIX, XPG4
difftime 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
This example shows a timing application using difftime.
The example calculates how long, on average, it takes to find the
prime numbers from 2 to 10000.
#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);
/************************************************************
The output should be similar to:
The program takes an average of 0.106000 seconds to
find 1229 prime.
************************************************************/
}
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asctime -- Convert Time to Character
String
ctime -- Convert Time to Character
String
gmtime -- Convert Time
localtime -- Convert Time
mktime -- Convert Local Time
strftime -- Convert to Formatted Time
time -- Determine Current Time
<time.h>