C 알고리즘 시간 측정방법

#include<stdio.h>
#include<time.h>
 
int main(void)
{
	/*알고리즘 수행시간 측정 방법1*/
	double start = clock();
	//... 내용
	int arr[5] = { 1,2,5,6,4 };
 
	for (int i = 0; i < 4; i++)
	{
		for (int j = i+1; j < 5; j++)
		{
			if (arr[i] < arr[j])
			{
				int tmp = arr[i];
				arr[i] = arr[j];
				arr[j] = tmp;
			}
		}
	}
	for (int i = 0; i < 5; i++)
	{
		printf("%d ", arr[i]);
	}
	double stop = clock();
	double duration = (double)(stop - start) / CLOCKS_PER_SEC;
 
 
	/*알고리즘 수행시간 측정 방법2*/
	double start2 = time(NULL);
	//...내용
	double stop2 = time(NULL);
	double duration2 = (double)difftime(stop2, start2);
 
	printf("duration1: %f ,  duration2:  %f  ", duration, duration2);
}

출력물.

6 5 4 2 1 duration1: 0.000045 , duration2: 0.000000