title: Convert const char* string to NSString with length AND encoding
body: <p>I wonder which method would be better to convert const char* string to NSString.<br/>
  I found there are some facts.</p>
  
  <ul>
  <li>[NSString stringWithCString:length:] is kind of deprecated.</li>
  <li>[NSString stringWithCString:encoding] may be used for my purpose</li>
  </ul>
  
  <p>But I want to convert with length AND encoding(because I want to make that fine if I have some Non-ASCII character by setting encoding to UTF-8). Any thoughts?</p>
  
  <p>I just think now</p>
  
  <ol>
  <li>create other char and copy with length by using std::strncpy(ch1, ch2, len)</li>
  <li>use [NSString stringWithCString:encoding:]</li>
  </ol>
  
  <p>But it doesn't work well.</p>