Change zmq_monitor_fn type to cast between pointer-to-object and…

Change zmq_monitor_fn type to cast between pointer-to-object and pointer-to-function in a more standards compliant way

doc/zmq_setsockopt.txt

@@ -434,7 +434,7 @@ Applicable socket types:: all listening sockets, when using TCP transports.
 ZMQ_MONITOR: Registers a callback for socket state changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Registers a callback function / event sink for changes in underlying socket state.
-Expected signature is `void (zmq_monitor_fn) (void *s, int event, zmq_event_data_t *data)`
+Expected signature of function member of zmq_monitor_fn union is `void (*function)(void *s, int event, zmq_event_data_t *data);`
 To remove the callback function call `zmq_setsockopt(socket, ZMQ_MONITOR, NULL, 0)`
 The default value of `NULL` means no monitor callback function.
 Supported events are :

include/zmq.h

@@ -300,7 +300,10 @@ typedef union {
 } zmq_event_data_t;
 
 /*  Callback template for socket state changes                                */
-typedef void (zmq_monitor_fn) (void *s, int event, zmq_event_data_t *data);
+typedef union {
+    void *object;
+    void (*function)(void *s, int event, zmq_event_data_t *data);
+} zmq_monitor_fn;
 
 ZMQ_EXPORT void *zmq_socket (void *, int type);
 ZMQ_EXPORT int zmq_close (void *s);

src/socket_base.cpp

@@ -1030,7 +1030,7 @@ void zmq::socket_base_t::monitor_event (int event_, ...)
         default:
             zmq_assert (false);
         }
-        options.monitor ((void *)this, event_, &data);
+        options.monitor->function ((void *)this, event_, &data);
         va_end (args);
     }
 }

tests/test_monitor.cpp

@@ -99,20 +99,20 @@ int main (int argc, char *argv [])
     assert (rep);
 
     // Expects failure - invalid size
-    zmq_monitor_fn *monitor;
-    monitor = listening_sock_monitor;
+    zmq_monitor_fn monitor;
+    monitor.function = listening_sock_monitor;
 
-    rc = zmq_setsockopt (rep, ZMQ_MONITOR, *(void **)&monitor, 20);
+    rc = zmq_setsockopt (rep, ZMQ_MONITOR, &monitor, 20);
     assert (rc == -1);
     assert (errno == EINVAL);
 
-    rc = zmq_setsockopt (rep, ZMQ_MONITOR, *(void **)&monitor, sizeof (void *));
+    rc = zmq_setsockopt (rep, ZMQ_MONITOR, &monitor, sizeof (void *));
     assert (rc == 0);
 
     size_t sz = sizeof (void *);
     rc = zmq_getsockopt (rep, ZMQ_MONITOR, &monitor, &sz);
     assert (rc == 0);
-    assert (monitor == listening_sock_monitor);
+    assert (monitor.function == listening_sock_monitor);
 
     // Remove socket monitor callback
     rc = zmq_setsockopt (rep, ZMQ_MONITOR, NULL, 0);
@@ -120,7 +120,7 @@ int main (int argc, char *argv [])
 
     rc = zmq_getsockopt (rep, ZMQ_MONITOR, &monitor, &sz);
     assert (rc == 0);
-    assert (monitor == listening_sock_monitor);
+    assert (monitor.function == listening_sock_monitor);
 
     rc = zmq_bind (rep, "tcp://127.0.0.1:5560");
     assert (rc == 0);
@@ -128,8 +128,8 @@ int main (int argc, char *argv [])
     void *req = zmq_socket (ctx, ZMQ_REQ);
     assert (req);
 
-    monitor = connecting_sock_monitor;
-    rc = zmq_setsockopt (req, ZMQ_MONITOR, *(void **)&monitor, sizeof (void *));
+    monitor.function = connecting_sock_monitor;
+    rc = zmq_setsockopt (req, ZMQ_MONITOR, &monitor, sizeof (void *));
     assert (rc == 0);
 
     rc = zmq_connect (req, "tcp://127.0.0.1:5560");