Calling SCardGetStatusChange

There seems to be a lot of confusion over just how to use the PC/SC SCardGetStatusChange service.  Here is an example of its proper use on Windows.

CardWatch.cpp

Note the following:

• First off, there's a special outer loop that uses an undocumented feature of the Windows PC/SC implementation -- the special reader name "\\?PNP?\Notification" gets events when smart card reader Plug 'n Play events occur.  It is used in an outer loop to rebuild the list of readers being watched.
• Within the inner loop, a DWORD named dwChanges is derived.  This DWORD contains flags that indicate what event has occurred.  For example, if the bit SCARD_STATE_PRESENT is set in dwChanges, then that means a change has occurred in the card present state for that reader.  Then your code would look at the SCARD_STATE_PRESENT bit in pRdr->dwEventState to see if the change is that a card became present, or a card was removed.
• Most confusion over the use of this call comes from getting too involved in the undefined bit states.  They're there only to help the Smart Card Subsystem -- your code shouldn't need to look at them!

A lot of people ask why it does things this way instead of using <insert your favorite event mechanism here>.  The reason is that when PC/SC designed it, we wanted it to be useable on multiple platforms.  The only common event mechanism we could find was to simply use threads.  Hence it assumes threads, and blocks until something happens.