C how to measure time correctly?
algorithm, c, measurement, performance, time
Solution
Two things:
`10000` is not a lot on a modern computer. Therefore that loop will run in probably less than a millisecond - less than the precision of `clock()`. Therefore it will return zero.
If you aren't using the result of `non_parallel` its possible that the entire loop will be optimized out by the compiler.
Most likely, you just need a more expensive loop. Try increasing `ARRAY_SIZE` to something much larger.
Here's a test on my machine with a larger array size:
#define ARRAY_SIZE 100000000
int main(){
clock_t start, end;
double *non_parallel = (double*)malloc(ARRAY_SIZE * sizeof(double));
double *vec = (double*)malloc(ARRAY_SIZE * sizeof(double));
start = clock();
for(int i = 0; i < ARRAY_SIZE; i++)
{
non_parallel[i] = vec[i] * vec[i];
}
end = clock();
printf( "Number of seconds: %f\n", (end-start)/(double)CLOCKS_PER_SEC );
free(non_parallel);
free(vec);
return 0;
}
Output:
Number of seconds: 0.446000
Problem
This is the "algorithm", but when I want to measure the execution time it gives me zero. Why? ``` #define ARRAY_SIZE 10000 ... clock_t start, end; start = clock(); for( i = 0; i < ARRAY_SIZE; i++) { non_parallel[i] = vec[i] * vec[i]; } end = clock(); printf( "Number of seconds: %f\n", (end-start)/(double)CLOCKS_PER_SEC ); ``` So What should i do to measure the time?