title: SCNetworkReachability compiling error
body: <p>I tried to compile Ercia Sadun's sample code <a href="http://github.com/erica/iphone-3.0-cookbook-/tree/master/C13-Networking/14-Web%20Browser/" rel="noreferrer">here</a>, but this error came up:</p>
  
  <pre><code>warning: in /Users/interdev/iphone source code/Web Browser/Classes/SystemConfiguration.framework/SystemConfiguration, missing required architecture i386 in file
      Undefined symbols:
        "_SCNetworkReachabilityScheduleWithRunLoop", referenced from:
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
        "_SCNetworkReachabilityCreateWithAddress", referenced from:
            +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
        "_SCNetworkReachabilityUnscheduleFromRunLoop", referenced from:
            +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
        "_SCNetworkReachabilitySetCallback", referenced from:
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
        "_SCNetworkReachabilityGetFlags", referenced from:
            +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
      ld: symbol(s) not found
      collect2: ld returned 1 exit status
          "_SCNetworkReachabilityScheduleWithRunLoop", referenced from:
              +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
          "_SCNetworkReachabilityCreateWithAddress", referenced from:
              +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
              +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
          "_SCNetworkReachabilityUnscheduleFromRunLoop", referenced from:
              +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
          "_SCNetworkReachabilitySetCallback", referenced from:
              +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
              +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
              +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
          "_SCNetworkReachabilityGetFlags", referenced from:
              +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
              +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
        ld: symbol(s) not found
        collect2: ld returned 1 exit status
      Build failed (5 errors)
  </code></pre>
  
  <p>...Even after I added systemConfiguration.framework, it reported the same error. Why did it do this, and how can I make it work?</p>