title: Question about character of NSString invalid in URL on iPhone
body: <p>Some of my http request has 'space' in URL, but it is not recognized by iPhone. I have to change 'space' to '%20' whenever there is a 'space' in the url. Now I have to send a message typed by the user to the server and it can have as many 'spaces' as the user like. It looks like I have to replace them all.(stringByReplacingOccurrencesOfString)</p>
  
  <p>Convert 'space' to '%20' is the one I occasionally find. My question is which of the other characters in NSString cannot be straightly used by url on iPhone?</p>