c++ - How To Return Elapsed Time From steady_clock as a Primitive Data Type (double)


First and foremost, let me say that I just starting using this library yesterday, so my understanding of it is still fairly basic. I'm trying to capture the FPS of a vision processing program I'm creating and output it to a screen using the chrono library. In my case, I need to cast the elapsed time taken after I start a steady_clock to a double (or some other numerical typedef I could treat like a double). I looked through reference documentation and tried working with the duration_cast and time_point_cast functions, but neither of those seem to be what I'm looking for.

My question is; is there any way to simply cast the numerical value of a clock's current state in seconds to a primitive data type?

Any help would be appreciated.

2 Answers: 

Like this:

#include <chrono>
#include <iostream>
#include <thread>

int main()
  using namespace std::literals;

  // measure time now
  auto start = std::chrono::system_clock::now();

  // wait some time

  // measure time again
  auto end = std::chrono::system_clock::now();

  // define a double-precision representation of seconds
  using fsecs = std::chrono::duration<double, std::chrono::seconds::period>;

  // convert from clock's duration type
  auto as_fseconds = std::chrono::duration_cast<fsecs>(end - start);

  // display as decimal seconds
  std::cout << "duration was " << as_fseconds.count() << "s\n";

example output:

duration was 1.00006s

You could do it using the duration::count function.

For example you could get the duration in the number of milliseconds, and then divide the count by 1000.0 to get the number of seconds as a double.


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