Why does clock() function in C from header only returns clock tick values in increments of 10's of thousands?

Asked Oct 12 '17 at 14:32

Active Oct 12 '17 at 15:38

Viewed 81 times

I am curious to know why does the function clock() only returns values in increments of 10,000 and is not able to return values in between.

I have the following code:

#include<iostream>
#include<time.h>
#include<stdio.h>
using namespace std;

int main()
{
    int a;
    clock_t clock_start;
    time_t start1;
    time(&start1);
    clock_start = clock();

    for(int i=0;i<200000;i++)
        cout<<8;

    time_t end1;
    time(&end1);

    clock_t clock_end = clock();

    int b;
    printf("\n\n%d",end1-start1);
    printf("\nClock ticks ?? = %d",clock_end-clock_start);
    return 0;
}

The result is either 0 or 10,000

There is no in-between.

The same situation is happening even if I modify the number of iterations the 'for' loop runs. The values are also multiple of 10,000

What is the reason behind this behavior and what is a practical use case for the "clock" function in this case? It seems quite unreliable to me.

edited Oct 12 '17 at 15:38

Jens Gustedt

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asked Oct 12 '17 at 14:32

On what platform are you running this? – Joe Oct 12 '17 at 14:34
Because that is the clock interval of your hardware clock. Background info: https://blogs.msdn.microsoft.com/oldnewthing/20170921-00/?p=97057 – Richard Critten Oct 12 '17 at 14:34
CentOS 6.5 on gcc – Oct 12 '17 at 14:34
@JenniferAnderson I meant what h/w platform... – Joe Oct 12 '17 at 14:35
@Joe Intel x86 but on VM – Oct 12 '17 at 14:36
... so, because of the **VM**. – Antti Haapala -- Слава Україні Oct 12 '17 at 14:39
Note that format specifer `%d` is incorrect for `time_t`. On my system `int` is size 4, and `time_t` is size 8. – Weather Vane Oct 12 '17 at 14:40
@AnttiHaapala what it is because of the VM ? The poor resolution of one second? How would it be different if I would run the code on an operating system that is naively installed on my computer? – Oct 12 '17 at 14:41

Why does clock() function in C from header only returns clock tick values in increments of 10's of thousands?

0 Answers0