What is the maximum time interval chrono can measure in C++?

Question

I'm quiet experienced in programming, but new to C++. I'm trying to measure the time it takes to run a code. In the future I might write code that can take hours/days to finish itself. Therefore it is important for me to know the limits of the chrono time measurement. Accuracy in milliseconds should be sufficient.

What is the maximum time I can measure?

I have used the following code, please let me know if this can be improved:

#include <chrono> 
using namespace std::chrono;

auto start = high_resolution_clock::now();

// calculations here

auto finish = high_resolution_clock::now();

duration<double> elapsed = finish - start; // elapsed time in seconds
cout << elapsed.count();

Answer 1

Here's an informative little HelloWorld:

#include <chrono>
#include <iostream>

int
main()
{
    using namespace std::chrono;
    using namespace std;

    using years = duration<double, ratio_multiply<ratio<86'400>, ratio<146'097, 400>>>;
    cout << years{high_resolution_clock::time_point::max() - 
                  high_resolution_clock::now()}.count()
         << " years until overflow\n";
}

I first create a double-based years duration so that the output is easy to read. Then I subtract now() from the time_point's max(), convert that to years and print it out.

For me this just output:

292.256 years until overflow