Convert string time to UNIX timestamp

Question

I have a string like 2013-05-29T21:19:48Z. I'd like to convert it to the number of seconds since 1 January 1970 (the UNIX epoch), so that I can save it using just 4 bytes (or maybe 5 bytes, to avoid the year 2038 problem). How can I do that in a portable way? (My code has to run both on Linux and Windows.)

I can get the date parts out of the string, but I don't know how to figure out the number of seconds. I tried looking at the documentation of date and time utilities in C++, but I didn't find anything.

Answer 1

use std::get_time if you want the c++ way - but both other options are also valid. strptime will ignore the Z at the end - and the T can be accomodated by format string %Y-%m-%dT%H:%M:%s - but you could also just put the Z at the end.

Answer 2

Here is the working code

string s{"2019-08-22T10:55:23.000Z"};
std::tm t{};
std::istringstream ss(s);

ss >> std::get_time(&t, "%Y-%m-%dT%H:%M:%S");
if (ss.fail()) {
    throw std::runtime_error{"failed to parse time string"};
}   
std::time_t time_stamp = mktime(&t);