std::time (3) - Linux Man Pages
Defined in header <ctime>
std::time_t time( std::time_t* arg );
Returns the current calendar time encoded as a std::time_t object, and also stores it in the object pointed to by arg, unless arg is a null pointer.
arg - pointer to a std::time_t object to store the time, or a null pointer
Current calendar time encoded as std::time_t object on success, (std::time_t)(-1) on error. If arg is not null, the return value is also stored in the object pointed to by arg.
The encoding of calendar time in std::time_t is unspecified, but most systems conform to POSIX_specification and return a value of integral type holding the number of seconds since the_Epoch. Implementations in which std::time_t is a 32-bit signed integer (many historical implementations) fail in the year 2038.
// Run this code
system_clock wall clock time from the system-wide realtime clock