Determining how many minutes have passed using two strings with two different set of time ?

[PolloLoco4645]

Write your question here.


Let's say I have two std::string that have two different times like so

12:05:02
12:20:02

in the HH:MM:SS format
how can I go about getting and storing how many minutes have passed between the two sets of time ? For example, a total of 15 minutes have passed between those two given times.

[Hengry]

Use the member function substr and convert the string into minutes using stoi and do your calculations

[gunnerfunner]

You can also use std::tm with std::chrono::duration_cast:

#include <iostream>
#include <string>
#include <chrono>
#include <sstream>
#include <iomanip>
#include <typeinfo>


int main()
{
    std::string timeStart = "12:05:02";
    std::string timeEnd = "12:20:02";

    std::tm tStart{}, tEnd{};
    //Structure holding a calendar date and time broken down into its components.
    //http://en.cppreference.com/w/cpp/chrono/c/tm

    std::istringstream streamStart(timeStart);
    std::istringstream streamEnd(timeEnd);

    streamStart >> std::get_time(&tStart, "%H:%M:%S");
    streamEnd >> std::get_time(&tEnd, "%H:%M:%S");
    //http://stackoverflow.com/questions/21021388/how-to-parse-a-date-string-into-a-c11-stdchrono-time-point-or-similar

    auto startTime = std::chrono::hours(tStart.tm_hour) + std::chrono::minutes(tStart.tm_min) + std::chrono::seconds(tStart.tm_sec);
    auto endTime = std::chrono::hours(tEnd.tm_hour) + std::chrono::minutes(tEnd.tm_min) + std::chrono::seconds(tEnd.tm_sec);
    //convert std::tm to std::duration for subtraction
    
    auto duration = endTime - startTime;
    
    auto hours   = std::chrono::duration_cast<std::chrono::hours>(duration);
    auto minutes = std::chrono::duration_cast<std::chrono::minutes>(duration - hours);
    auto seconds = std::chrono::duration_cast<std::chrono::seconds>(duration - minutes);
    //Converts a std::chrono::duration to a duration of different type
    //http://en.cppreference.com/w/cpp/chrono/duration/duration_cast
     
    std::tm t{};
   
    t.tm_hour = hours.count();
    t.tm_min  = minutes.count();
    t.tm_sec = seconds.count();

    std::cout << std::put_time(&t, "%H:%M:%S") << '\n';
    //http://en.cppreference.com/w/cpp/io/manip/put_time
}

http://coliru.stacked-crooked.com/a/fb5242db568813fe

[JLBorges]

int seconds_since_midnight( std::string t ) // format is hh:mm:ss (24 hr clock)
{ return std::stoi(t) * 60*60 + std::stoi( t.substr(3) ) * 60 + std::stoi( t.substr(6) ) ; }

int elapsed_completed_minutes( std::string from, std::string to ) // format is hh:mm:ss (24 hr clock)
{
    const auto a = seconds_since_midnight(from) ;

    auto b = seconds_since_midnight(to) ;
    if( b < a ) b += 24*60*60 ; // period crosses over midnight

    return (b-a) / 60 ;
}

http://coliru.stacked-crooked.com/a/bbffa9b005526432