title: MVC validation question
body: <p>I have just starting learning the MVC pattern today (for gui applications, not web), and have a few questions on where data validation should take place.</p>
  
  <p>From what i have read, it seems like most people are saying that all the validations should take place on the controller, and the model should pretty much only hold the state of the data. However, it seems like in some situations it would make more sense to do the verification in the model. </p>
  
  <p>For example, lets say that a client changes the ipv4 address of the server they want to connect to from the gui. We want to verify that this is in fact an ipv4 address, and not just random characters. If the ip address is valid, then we want to change that data in the model to the new ip address, and if it isn't valid we want to have the view display an error (or something).</p>
  
  <p>If you did the verification in the controller, then if in the future you decided you wanted to have a different controller/view (because from what i can tell, they are coupled pretty closely together), you would have to make sure to include this same verification code in both controllers, and would thus have to manage two pieces of the same code. That would of course be more prone to bugs then managing just one piece of code, like if the verification was done in the model.</p>
  
  <p>Should i be doing it this way? Or am i missing that makes doing it in the controller make more sense? Or should some data be handled in the model, and some data handled in the controller?</p>
  
  <p>Thanks</p>