The FCS-at-end flag was being ignored in RadioTap. Added beacon display example.

examples/beacon_display.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+#include <map>
+#include <string>
+#include <tins/tins.h>
+
+using namespace Tins;
+
+class BeaconSniffer {
+public:
+    void run(const std::string &iface);
+private:
+    typedef Dot11::address_type address_type;
+    typedef std::map<address_type, std::string> ssids_type;
+
+    bool callback(PDU &pdu);
+    
+    ssids_type ssids;
+};
+
+void BeaconSniffer::run(const std::string &iface) {
+    Sniffer sniffer(iface, 1500, true, "type mgt subtype beacon");
+    sniffer.sniff_loop(make_sniffer_handler(this, &BeaconSniffer::callback));
+}
+
+bool BeaconSniffer::callback(PDU &pdu) {
+    Dot11Beacon *beacon = pdu.find_pdu<Dot11Beacon>();
+    if(beacon && !beacon->from_ds() && !beacon->to_ds()) {
+        address_type addr = beacon->addr2();
+        ssids_type::iterator it = ssids.find(addr);
+        if(it == ssids.end()) {
+            try {
+                it = ssids.insert(std::make_pair(addr, beacon->ssid())).first;
+                std::cout << it->first << " - " << it->second << std::endl;
+            }
+            catch(std::runtime_error&) {
+                // no ssid, just ignore it.
+            }
+        }
+    }
+    return true;
+}
+
+int main(int argc, char* argv[]) {
+    std::string interface = "wlan0";
+    if(argc == 2)
+        interface = argv[1];
+    BeaconSniffer sniffer;
+    sniffer.run(interface);
+}