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 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); } /******************** Output should be similar: ***************** The program takes an average of 0.106000 seconds to find 1229 primes. */
Related Information
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