I'm trying to get current date and time in cpp but can't understand these lines

Question

Pls can anybody explain me these two lines

// Current date/time based on current system


time_t now = time(0);

// Convert now to tm struct for local timezone


tm* localtm = localtime(&now);

Answer 1

That is a very old C-styled way of determining local date & time based on time.h. The documentation for that header file explains a lot, but to summarize, time() returns a system-time in seconds from Epoch (00:00 on 1-Jan-1970) when passed a null pointer (hence the zero), or time from another set time_t instance. The pointer here is essential because it drives different behaviors of the function based on the pointer value.

localtime() takes system-time information and converts it to a local-time based upon current system settings. I've never been sure why this took a pointer as an argument, but I assume it's just to maintain consistency with the API.

A better, more C++ way of getting local-time is to use the std::chrono library (http://www.cplusplus.com/reference/chrono/?kw=chrono). You could get higher resolution local-time (instead of just accurate to the nearest second), without pointer-jockeying. For example, please refer to: Outputting Date and Time in C++ using std::chrono