title: How set the date formatter to NSDate and assign the result value to NSDate
body: <p>I want to save the the current date and time in GMT in my core data. The field for current date in the table is set as Date field. I have no chance to change the field in to <code>NSString</code>.</p>
  
  <pre><code>NSDate *memberShipDate = [NSDate dateWithTimeIntervalSince1970:[intervalString doubleValue]];          
  NSTimeZone *gmt = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
  [formatter setTimeZone:gmt];    
  NSString *newmemberShipDate = [formatter stringFromDate:memberShipDate];
  </code></pre>
  
  <p>Here the <code>newmemberShipDate</code> is in <code>NSString</code> format. When I am trying to save this data to my db, it will become error. I need the  <code>newmemberShipDate</code> in <code>NSDate</code> format.</p>