Include files not working in PHP despite file existing?

Question

Trying to include file in .php file:

<?php 
   $lesson = $_GET["lesson"];
   include_once($lesson + "_title.php"); 
?>

But for some reason I keep getting this error:

Warning: include_once(0): failed to open stream: No such file or directory in C:\xampp\htdocs\Periodic Tutor\layout.php on line 10

Warning: include_once(): Failed opening '0' for inclusion (include_path='.;\xampp\php\PEAR') in C:\xampp\htdocs\Periodic Tutor\layout.php on line 10

It keeps showing that the file doesn't exist, yet it does. I have done an echo statement to check the arguments being passed to the include function and the string is correct.

I am using XAMPP as my testing server and Dreamweaver, but PHP url variables and include/require statements have never been a problem before.

Any suggestions? Thanks!

Answer 1

When concatenating a string, you use "." not "+". include_once($lesson."_title.php");

Keep in mind that including things that way is a bit dangerous as people could use absolute paths in $_GET["lesson"] to include things that could be private.

Answer 2

In this line:

include_once($lesson + "_title.php");

You're arithmetically adding the two terms, which gives a result of zero.

Do this:

include_once($lesson . "_title.php");