Process Timing Discrepancies - c++

Question

Let me start by saying, I am not a skilled C++ programmer, I have just begun that journey and am working in a Win 10 environment using Code::Blocks as my ide. I am starting to learn C++ by coding solutions to the Euler Project problems. I used these problems to start learning Python several years ago, so I have at least one Python solution for the first 50+ problems. In doing these problems in Python, I learned that as my skill improves, I can formulate better solutions. When learning Python, I used a trial & error approach to improving my code until I became aware of the python tools for timing my code. Once, I defined a convenient and consistent timing method, my coding improved dramatically. Since, I am beginning this journey now with C++ I decided I would be proactive and create a consistent method for timing the code execution. To do this, I have decided to utilize the C++ chrono library and have defined two different approaches that seemingly should produce the same time results. However as the tile to this question implies they don't.
So here's my question: Why don't the following two approaches yield the same results?
Approach # 1
This method provides a timing for the do some stuff segment of slightly over 3 seconds, but less than the CODE::BLOCKS execution time report of 3.054 seconds. I certainly understand these differences based on the program flow. So this approach seems to give good result. The issue I have with this approach is I need to copy & paste the timing code into each .cpp file I want to time, which seems sloppy.
Output using this method looks like the following:
Elapsed time in seconds : 3.00053 sec
Process returned 0 (0x0) execution time : 3.151 s
#include <iostream>
#include <chrono>
#include <unistd.h>
using namespace std;
using Clock = chrono::steady_clock;
using TimePoint = chrono::time_point<Clock>;
// Functions
TimePoint get_timestamp();
double get_duration(TimePoint, TimePoint);
int main()
{
//auto start = chrono::steady_clock::now();
auto start_t = get_timestamp();
//cout << "Start is of type " << typeid(start).name() << "\n";
// do some stuff
sleep(3);
auto end_t = get_timestamp();
//double tme_secs = chrono::duration_cast<chrono::nanoseconds>(end - start).count()/1000000000.0000;
double tme_secs = get_duration(start_t, end_t)/1000000000;
cout << "Elapsed time in seconds : " << tme_secs << " sec";
return 0;
}
TimePoint get_timestamp(){
return Clock::now();
}
double get_duration(TimePoint start, TimePoint end){
return chrono::duration_cast<chrono::nanoseconds>(end - start).count()*1.00000000;
}
Approach #2
In this approach, I attempted to create a ProcessTime class which could be included in files that I want to time and provide a cleaner method. The problem with this approach is I get timing report in the nano seconds, which does not reflect the process being timed. Here is my implementation of this approach.
output using this method looks like the following:
Elapsed time: 1.1422e+06 seconds
Process returned 0 (0x0) execution time : 3.148 s
ProcessTime.h file
#ifndef PROCESSTIME_H_INCLUDED
#define PROCESSTIME_H_INCLUDED
#include <chrono>
using namespace std;
using Clock = chrono::steady_clock;
using TimePoint = chrono::time_point<Clock>;
class ProcessTime{
public:
ProcessTime();
double get_duration();
private:
TimePoint proc_start;
};
#endif // PROCESSTIME_H_INCLUDED
ProcessTime.cpp file
#include "ProcessTime.h"
#include <chrono>
using namespace std;
using Clock = chrono::steady_clock;
using TimePoint = chrono::time_point<Clock>;
ProcessTime::ProcessTime(){
TimePoint proc_start = Clock::now();
}
double ProcessTime::get_duration(){
TimePoint proc_end = Clock::now();
return chrono::duration_cast<chrono::nanoseconds>(proc_end - ProcessTime::proc_start).count()*1.00000000;
}
main.cpp file:
#include <iostream>
#include "ProcessTime.h"
#include <unistd.h>
using namespace std;
int main()
{
ProcessTime timer;
// Do some Stuff
sleep(3);
double tme_secs = timer.get_duration()/1000000000;
cout << "Elapsed time: " << tme_secs << " seconds";
return 0;
}

Answer 1

This is incorrect:
ProcessTime::ProcessTime(){
TimePoint proc_start = Clock::now();
}
You are setting a local variable named proc_start, and then the constructor ends. You did not set the actual member variable of ProcessTime.
One fix (and the preferred method) is to use the member-initialization list:
ProcessTime::ProcessTime() : proc_start(Clock::now()) {}
or if you knew nothing about the member-initialization list, the code would look like this to assign the value.
ProcessTime::ProcessTime(){
proc_start = Clock::now();
}