C++ :: Program Which Takes Date And Time Input From The User

I am writing a C++ program which takes date & time input from the user. This is then parsed into a struct such as:

struct time
{
short year;
short month;
short day;
short hour;
short min;
};

My question is: how can I convert such a struct into a time_t object, which is an unsigned long giving the time as the number of seconds elapsed since the epoch Jan 1st 1970, 00:00, as set out in time.h.

I am wondering if this can be achieved using the standard library, or whether I just need to write a function to perform the appropriate arithmetic.