QueryPerformanceCounter returning negative number - c++

Question

Hey im trying to count how long the function takes to execute
I am doing it like this:
Timer.cpp
long long int Timer :: clock1()
{
QueryPerformanceCounter((LARGE_INTEGER*)&time1);
return time1;
}
long long int Timer :: clock2()
{
QueryPerformanceCounter((LARGE_INTEGER*)&time2);
return time2;
}
main.cpp
#include "Timer.h" //To allow the use of the timer class.
Timer query;
void print()
{
query.clock1();
//Loop through the elements in the array.
for(int index = 0; index < num_elements; index++)
{
//Print out the array index and the arrays elements.
cout <<"Index: " << index << "\tElement: " << m_array[index]<<endl;
}
//Prints out the number of elements and the size of the array.
cout<< "\nNumber of elements: " << num_elements;
cout<< "\nSize of the array: " << size << "\n";
query.clock2();
cout << "\nTime Taken : " << query.time1 - query.time2;
}
Can anyone tell me if i am doing this correctly?

Answer 1

You are substracting ending time from starting time.
cout << "\nTime Taken : " << query.time1 - query.time2;
should be
cout << "\nTime Taken : " << query.time2 - query.time1

Answer 2

Let's say I start something at 10 seconds and it finishes at 30 seconds. How long did it take? 20 seconds. To get that, we would do 30 - 10; that is, the second time subtract the first time.
So perhaps you want:
cout << "\nTime Taken : " << (query.time2 - query.time1);