Updated Examples and Recipes (markdown)

Examples-and-Recipes.md

@@ -5,6 +5,7 @@ This page contains examples and recipes contributed by community members. Feel f
 - [The current time somewhere else](#elsetime)
 - [Get the current difference between any two arbitrary time zones](#deltatz)
 - [Set simultaneous meeting in two different time zones](#meeting)
+- [Get milliseconds since the local midnight](#since_midnight)
 - [Obtaining a `time_point` from `y/m/d h:m:s` components](#time_point_to_components)
 - [Obtaining `y/m/d h:m:s` components from a `time_point`](#components_to_time_point)
 - [Normalizing `y/m/d` when it is `!ok()`](#normalize)
@@ -157,6 +158,101 @@ In any event, the output is still:
     2016-07-08 09:00:00 EDT
     2016-07-08 16:00:00 MSK
 
+<a name="since_midnight"></a>
+### Get milliseconds since the local midnight
+(by [Howard Hinnant](https://github.com/HowardHinnant))
+
+After reading this [stack Overflow question/answers](http://stackoverflow.com/q/11128629/576911) I decided it would be good to show how to solve this problem using this library.  As the question is not crystal clear what it is asking, I will attempt to create an unambiguous problem statement here:
+
+> Find the time duration in milliseconds since the last midnight in the local time zone.
+
+So that I can more easily test the code to do this, I'm going to write this more generally as:
+
+    std::chrono::milliseconds
+    since_local_midnight(std::chrono::system_clock::time_point t, const date::time_zone* zone);
+
+And then create an overload to pass in the current time and current time zone:
+
+    inline
+    std::chrono::milliseconds
+    since_local_midnight()
+    {
+        return since_local_midnight(std::chrono::system_clock::now(), date::current_zone());
+    }
+
+That way I can test things like times just after known daylight saving time transitions to make sure that my code is doing what I want it to.
+
+This only takes a few lines of code:
+
+    std::chrono::milliseconds
+    since_local_midnight(std::chrono::system_clock::time_point t, const date::time_zone* zone)
+    {
+        using namespace date;
+        using namespace std::chrono;
+        auto zt = make_zoned(zone, t);
+        zt = floor<days>(zt.get_local_time());
+        return floor<milliseconds>(t - zt.get_sys_time());
+    }
+
+The first thing to do is create a `zoned_time` which really does nothing at all but pair `zone` and `t`.  This pairing is mainly just to make the syntax nicer.
+
+The next step is to get the local time associated with `t`.  That is what `zt.get_local_time()` does.  This will have whatever precision `t` has, unless `t` is coarser than seconds, in which case the local time will have a precision of seconds.
+
+The call to `floor<days>` _truncates_ the local time to a precision of `days`.  This effectively creates a `local_time` equal to the local midnight.  By assigning this `local_time` back to `zt`, we don't change the time zone of `zt` at all, but we change the `local_time` of `zt` to midnight (and thus change its `sys_time` as well).
+
+We can get the corresponding `sys_time` out of `zt` with `zt.get_sys_time()`.  This is the UTC time which corresponds to the local midnight.  It is then an easy process to subtract this from the input `t` and truncate the results to the desired precision.
+
+As a further testing aid, it is convenient to write a `since_local_midnight` that takes a `zoned_seconds` (which is a `zoned_time` with the precision of seconds) that calls into the main overload:
+
+    inline
+    std::chrono::milliseconds
+    since_local_midnight(const date::zoned_seconds& zt)
+    {
+        return since_local_midnight(zt.get_sys_time(), zt.get_time_zone());
+    }
+
+So to output the current time in milliseconds since the local midnight, you would just:
+
+    std::cout << since_local_midnight().count() << "ms\n";
+
+To ensure that our function is working, it is worthwhile to output a few example dates.  This is most easily done by specifying a time zone (I'll use "America/New_York"), and some local date/times where I know the right answer:
+
+    auto zt = make_zoned(locate_zone("America/New_York"), local_days{jan/15/2016} + 3h);
+    std::cout << zt << " is " << since_local_midnight(zt).count() << "ms after midnight\n";
+
+This 3am in the middle of the Winter.  This outputs:
+
+    2016-01-15 03:00:00 EST is 10800000ms after midnight
+
+which is correct (10800000ms == 3h).
+
+I can run the test again just by assigning a new local time to `zt`.  The following is 3am just after the "spring forward" daylight saving transition (2nd Sunday in March):
+
+    zt = local_days{sun[2]/mar/2016} + 3h;
+    std::cout << zt << " is " << since_local_midnight(zt).count() << "ms after midnight\n";
+
+This outputs:
+
+    2016-03-13 03:00:00 EDT is 7200000ms after midnight
+
+Because the local time from 2am to 3am was skipped, this correctly outputs 2 hours since midnight.
+
+An example from the middle of Summer gets us back to 3 hours after midnight:
+
+    zt = local_days{jul/15/2016} + 3h;
+    std::cout << zt << " is " << since_local_midnight(zt).count() << "ms after midnight\n";
+
+    2016-07-15 03:00:00 EDT is 10800000ms after midnight
+
+And finally an example just after the Fall transition from daylight saving back to standard gives us 4 hours:
+
+    zt = local_days{sun[1]/nov/2016} + 3h;
+    std::cout << zt << " is " << since_local_midnight(zt).count() << "ms after midnight\n";
+
+    2016-11-06 03:00:00 EST is 14400000ms after midnight
+
+Not only does this library make it easy to write the code to do the desired computation, it also makes it easy to write the test code.
+
 <a name="time_point_to_components"></a>
 ### Obtaining a `time_point` from `y/m/d h:m:s` components
 (by [ecorm](https://github.com/ecorm))