title: How do I convert a NSString into TIS-620 encoded string
body: <p>In the apple document, I can see that there's a way to convert from UTF8 string to ASCII string like this</p>
  
  <pre><code>NSData *asciiData = [theString dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
  NSString *asciiString = [[NSString alloc] initWithData:asciiData encoding:NSASCIIStringEncoding];
  </code></pre>
  
  <p>But my app requires a TIS-620 string to post to a site so I try to do the same thing</p>
  
  <pre><code>NSData *asciiData = [newPost.header dataUsingEncoding:kCFStringEncodingMacThai allowLossyConversion:YES];
  NSString *asciiString = [[NSString alloc] initWithData:asciiData encoding:kCFStringEncodingMacThai];
  NSLog(@"%@", asciiString);
  </code></pre>
  
  <p>The output I got is like this ???????????.</p>
  
  <p>Does anyone know how to convert the NSString to TIS-620 properly? 
  Thanks so much.</p>