title: I'm trying to find a file size. But my length is equl to zero
body: <p>I'm trying to find a file size.</p>
  
  <pre><code> NSFileHandle *output = [NSFileHandle fileHandleForWritingAtPath:self.finalPath]; 
  //seek to begin of the file
  [output seekToFileOffset:0];
  NSData *mydata = [output availableData];
  NSLog(@"length: %d", [mydata length]);
  </code></pre>
  
  <p>But my length is equl to zero. Why?</p>