Updated Examples and Recipes (markdown)

Examples-and-Recipes.md

@@ -27,6 +27,7 @@ This page contains examples and recipes contributed by community members. Feel f
 - [How to convert to/from C++ Builder's TDate and TDateTime](#TDate)
 - [How to convert to/from QDate](#QDate)
 - [How to convert to/from Windows' FILETIME](#fILETIME)
+- [How to convert to/from boost::posix_time::ptime](#ptime)
 - [Print out a compact calendar for the year](#calendar)
 - [Parsing unambiguous date time inside daylight transition](#parse_daylight_transition)
 - [`microfortnights`?!  Are you serious?](#microfortnights)
@@ -1724,6 +1725,52 @@ FILETIME system_clock_to_FILETIME(system_clock::time_point systemPoint) {
     return result;
 }
 ```
+<a name="ptime"></a>
+### How to convert to/from `boost::posix_time::ptime`
+(by [Howard Hinnant](https://github.com/HowardHinnant))
+
+`boost::posix_time::ptime` and `std::chrono::system_clock::time_point` represent the same thing in their respective libraries (boost and chrono).  So it is nice to be able to convert between them.  This is how to do it:
+
+```c++
+#include "boost/date_time/posix_time/posix_time.hpp"
+#include "date/date.h"
+
+std::chrono::system_clock::time_point
+to_system_clock(boost::posix_time::ptime const& pt)
+{
+    using namespace std::chrono;
+    auto const dt = pt - boost::posix_time::from_time_t(0);
+#ifdef BOOST_DATE_TIME_HAS_NANOSECONDS
+    std::chrono::nanoseconds ns{dt.total_nanoseconds()};
+    return system_clock::time_point{duration_cast<system_clock::duration>(ns)};
+#else
+    std::chrono::microseconds us{dt.total_microseconds()};
+    return system_clock::time_point{us};
+#endif
+}
+
+boost::posix_time::ptime
+to_ptime(std::chrono::system_clock::time_point const& st)
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto sd = floor<days>(st);
+    year_month_day ymd = sd;
+    hh_mm_ss<system_clock::duration> hms{st - sd};
+    auto y = int(ymd.year());
+    auto m = unsigned(ymd.month());
+    auto d = unsigned(ymd.day());
+    auto h = hms.hours().count();
+    auto M = hms.minutes().count();
+    auto s = hms.seconds().count();
+#ifdef BOOST_DATE_TIME_HAS_NANOSECONDS
+    auto fs = nanoseconds(hms.subseconds()).count();
+#else
+    auto fs = duration_cast<microseconds>(hms.subseconds()).count();
+#endif
+    return {{y, m, d}, {h, M, s, fs}};
+}
+```
 
 <a name="calendar"></a>
 ### Print out a compact calendar for the year