Error trying getting clock resolution time - c

Question

I'm using C and I'm trying to get Clock resolution but I get this value: 0.000000
Here is the code I'm using
#include <time.h>
#include<stdio.h>
double duration(struct timespec start, struct timespec end) {
return end.tv_sec - start.tv_sec
+ ((end.tv_nsec - start.tv_nsec ) / (double) 1000000000.0);
}
double getResolution(){
struct timespec start, end;
clock_gettime(CLOCK_MONOTONIC, &start);
do {
clock_gettime(CLOCK_MONOTONIC, &end);
} while (duration(start, end) == 0.0);
return duration(start, end);
}
int main(){
printf("%f",getResolution());
return 0;
}

Answer 1

You need to increase the precision in your printf("%f");. Using printf("%.12f"); would probably be enough to show some non-zero decimals.
Calculating the floating point duration in the while loop may cause the program to actually perform that calculation if the compiler isn't clever enough to figure out that you only need to see if the clock has changed at all. You could just do a memcmp to compare start and end instead.
Don't take the struct timespecs by value in your duration function. Supply pointers to the function instead. It should be cheaper.
Use the clock_getres function to get the resolution. The runtime value you get with your homebrewed solution depends on what speed the CPU is currently running at etc.
Example:
#include <stdio.h>
#include <string.h>
#include <time.h>
// taking the arguments via pointers:
double duration(const struct timespec* start, const struct timespec* end) {
return end->tv_sec - start->tv_sec +
((end->tv_nsec - start->tv_nsec) / 1000000000.0);
}
double getResolution() {
struct timespec start = {0}, end = {0};
clock_gettime(CLOCK_MONOTONIC, &start);
do {
clock_gettime(CLOCK_MONOTONIC, &end);
// using memcmp below:
} while (memcmp(&start, &end, sizeof start) == 0);
return duration(&start, &end);
}
int main() {
struct timespec base = {0}, res;
// using the proper function to get the resolution:
clock_getres(CLOCK_MONOTONIC, &res);
// comparing the results:
printf("clock_getres = %.12f\n", duration(&base, &res));
printf("getResolution = %.12f\n", getResolution());
}
Demo