Localhost url not working in iframe

I have a question on local host url in iframe.

I does not seem to pick the url up

PHP Code:

<iframe id="question-iframe" width="800" height="800"  src="<?php echo base_url();?>" class="form-control" allowfullscreen="true" ></iframe> 


It works fine with

PHP Code:

<iframe id="question-iframe" width="800" height="800"  src="http://www.w3schools.com" class="form-control" allowfullscreen="true" ></iframe> 


But just not localhost how can I display that with a localhost url?

There's only one rule - please don't tell anyone to go and read the manual.  Sometimes the manual just SUCKS!