How to convert epoch count in milliseconds to chrono time_point

Question

I am trying to convert epoch count in milliseconds (e.g., 1699491717000) to a C++ chrono time_point. I have tried the following commands and none of them worked for me.

1. I tried Howard Hinnant solution but the compiler did not like it

   std::chrono::system_clock::time_point tp{std::chrono::milliseconds{epoch_count_ms}};
   // Compiler says
   // No matching constructor for initialization of 'std::chrono::milliseconds' (aka 'duration<long, ratio<1, 1000>>')
   

2.  std::chrono::milliseconds epoch_duration(epoch_count_ms);
    std::chrono::system_clock::time_point tp(epoch_duration);
    // Compiler says:
    // No matching constructor for initialization of 'std::chrono::milliseconds' (aka 'duration<long, ratio<1, 1000>>') 
   

Could someone kindly help me out?

Answer 1

epoch_count_ms must be an integral type. If it is a double or a string, it will result in the error message you are seeing.

The second informational error message after the one you posted should contain this information, e.g.:

note: candidate constructor (the implicit copy constructor) not viable:
no known conversion from 'double' to 'const std::chrono::duration<long long, std::ratio<1, 1000>>' for 1st argument class _LIBCPP_TEMPLATE_VIS duration
                          ^^^^^^

This works:

long long epoch_count_ms = 1699491717000;
std::chrono::system_clock::time_point tp{std::chrono::milliseconds{epoch_count_ms}};