how can i use fopen() with CodeIgniter?

[eluser]chengfeng[/eluser]
Thanks for your comment! I have 2 websites. I want to use the second project(CI) to read a text file from the first project. When i use fopen() with CI, it doesn't work and so the error above. Then i test my code by copy it and write as stand-alone PHP script, It can be open and echo any text from the text file. These 2 websites are different hosting.
Sorry for bad English. And please tell me if you don't understand. Please!
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$filename="http://www.example.com/text.txt";
$file = fopen($filename,"r");
echo fread($file,100);
fclose($file);
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