c++ - How to reset chrono::duration value? -

i want collect runtime of program in pieces of codes(separate functions), current strategy calculate execution time(chrono::duration) each part , sum them together. have deal 2 different cases(call functions twice different input), , use static variable timer keep separated durations. wan reset variable before second case. how can this? of course can use duration of 2 consecutive system_clock::now(), seems unnecessary. tried timer = 0 or timer(0), doesn't work. example:

class myclass {   static std::chrono::milliseconds timer_a;   void foo();   void bar(); } 

in cpp file:

std::chrono::milliseconds timer_a(0); foo() {   ...   // someduration1;   timer_a += someduration1;   .... } bar() {   ...   // someduration2;   timer_a += someduration2;   ...   cout << timer_a.count(); } 

there main() call foo() , bar() twice. i.e.,

int main() {   if(somecondition) {     foo();     bar();   }   if(othercondition) {     // here need reset timer_a 0 s.t. record runtime again, how        ??????????     foo();     bar();   } 

my answer abit late here goes:

timer_a = std::chrono::miliseconds::zero(); 

you can create duration template use zero() function, way don't have know duration measured in (see below).

chrono doesn't have own timer class can create 1 easily:

//---------------------------------------------------------------- /* timer simple timer class using c++11 chrono. example use: {     timer_t t; // use global typedef standard timer.     t.start(); // start timer.     ... want time ...     t.end();   // end timer     t.calcduration; // calculate , store (inside timer class) interval between start , end.     cout << "time in milliseconds: " << t.getduration().count() << end; // cout interval } */ template< typename precision = long double, typename ratio = std::milli > class timer final { public:     //---------------- aliases ----------------     using timeduration_t = std::chrono::duration<precision, ratio>;     using timepoint_t = std::chrono::time_point<std::chrono::system_clock, timeduration_t>;     using this_type = timer< precision, ratio >;      //---------------- special member functions ----------------     // note: default compiler generated member functions suffice.      //---------------- member functions ----------------      //--------------------------------     /* start()         starts timer.     */     inline void start()     {         m_start = std::chrono::system_clock::now();     }      //--------------------------------     /* end()         ends timer.     */     inline void end()     {         m_end = std::chrono::system_clock::now();     }      //--------------------------------     /* calcduration()         calculates time elapsed (duration)         in between previous calls start , end().          note: make sure have called start() , end() before calling function.         note: start() , end() can called in order.     */     void calcduration()     {         m_duration = std::max( m_start, m_end ) - std::min( m_start, m_end );     }      //--------------------------------     /* getduration()         returns calculated duration.          note: make sure call calcduration() before calling function.     */     timeduration_t const& getduration() const     {         return m_duration;     }      //--------------------------------     /* zero()         zeros internal members, resetting timer.     */     void zero()     {         m_start = timeduration_t::zero();         m_end = m_start;         m_duration = m_end;     }      //--------------------------------     /* testlatency( i_count )         tests latency / error of timer class.          note: number how inaccurate timings can be.     */     static timeduration_t testlatency( size_t const i_count = 512 )     {         this_type t;         timeduration_t tsum = timeduration_t::duration::zero();         for( size_t = 0; < i_count; ++i )         {             t.start();             t.end();             t.calcduration();             tsum += t.getduration();         }         return tsum / i_count;     }  private:     //---------------- private member data ----------------     timepoint_t     m_start;     timepoint_t     m_end;     timeduration_t  m_duration; };  using timer_t = timer<>;