c++ - Persisting std::chrono time_point instances -

what correct way persist std::chrono time_point instances , read them instance of same type?

   typedef std::chrono::time_point<std::chrono::high_resolution_clock> time_point_t;     time_point_t tp = std::chrono::high_resolution_clock::now();    serializer.write(tp);    .    .    .    time_point_t another_tp;    serializer.read(another_tp); 

the calls write/read, assume instance of type time_point_t, can somehow converted byte representation, can written or read disk or socket etc.

a possible solution suggested alf follows:

   std::chrono::high_resolution_clock::time_point t0 = std::chrono::high_resolution_clock::now();     //generate pod write disk    unsigned long long ns0 = t0.time_since_epoch().count();     //read pod disk , attempt instantiate time_point    std::chrono::high_resolution_clock::duration d(ns0)     std::chrono::high_resolution_clock::time_point t1(d);     unsigned long long ns1 = t1.time_since_epoch().count();     if ((t0 != t1) || (ns0 != ns1))    {       std::cout << "error time points don't match!\n";    } 

note: above code has bug final instantiated time point not match original.

in case of of old style time_t, 1 typically writes entire entity disk based on sizeof , reads same way - in short equivalent new std::chrono types?

the time_point constructor takes duration, , can duration member time_since_epoch. question reduces serialize duration value. , duration has constructor takes number of ticks, , member function count produces number of ticks.

all googling std::chrono::time_point , looking @ cppreference documentation google landed me on.

it's idea read documentation.

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addendum: example.

#include <chrono> #include <iostream> #include <typeinfo> using namespace std;  auto main() -> int {     using clock = chrono::high_resolution_clock;     using time_point = clock::time_point;     using duration = clock::duration;      time_point const t0 = clock::now();      //generate pod write disk     duration::rep const ns0 = t0.time_since_epoch().count();      //read pod disk , attempt instantiate time_point     duration const d(ns0);     time_point const t1(d);      cout << "basic number type " << typeid( ns0 ).name() << "." << endl;     if( t0 != t1 )     {         cout << "error time points don't match!" << endl;     }     else     {         cout << "reconstituted time ok." << endl;     } } 

with visual c++ 12.0 reported basic type __int64, i.e. long long, while g++ 4.8.2 in windows reported type x, presumably means same.

with both compilers reconstituted time identical original.

addendum: noted dina in comments, of c++14 c++ standard doesn't specify epoch, , make work across machines or different clocks it's necessary add additional steps normalize epoch serialized data, e.g. , naturally posix time, i.e. time since since 00:00:00 coordinated universal time (utc), thursday, 1 january 1970.