zmq_errno helper function added

bindings/c/zmq.h

@@ -211,6 +211,16 @@ typedef struct
 
 ZMQ_EXPORT int zmq_poll (zmq_pollitem_t *items, int nitems, long timeout);
 
+////////////////////////////////////////////////////////////////////////////////
+//  Experimental.
+////////////////////////////////////////////////////////////////////////////////
+
+//  This function retrieves the errno as it is known to 0MQ library. The goal
+//  of this function is to make the code 100% portable, including where 0MQ
+//  compiled with certain CRT library (on Windows) is linked to an application
+//  compiled with different CRT library.
+int zmq_errno ();
+
 ////////////////////////////////////////////////////////////////////////////////
 //  Helper functions.
 ////////////////////////////////////////////////////////////////////////////////

src/zmq.cpp

@@ -615,6 +615,11 @@ int zmq_poll (zmq_pollitem_t *items_, int nitems_, long timeout_)
 #endif
 }
 
+int zmq_errno ()
+{
+    return errno;
+}
+
 #if defined ZMQ_HAVE_WINDOWS
 
 static uint64_t now ()