title: objective-c stringvalue from double
body: <p>I have the following code:</p>
  
  <pre><code>double d1 = 12.123456789012345;
  
  NSString *test1 = [NSString stringWithFormat:@"%f", d1]; // string is: 12.123457
  
  NSString *test1 = [NSString stringWithFormat:@"%g", d1]; // string is: 12.1235
  </code></pre>
  
  <p>How do I get a string value that is exactly the same as d1?</p>