Drupal and Global Variable

Today I found a problem with Drupal. I embedded my snippet code to Page content which will be include my project file. The structure is like below

/ (Drupal)

/project/setting.php

/project/interface.php

My drupal snippet code is "include(/project/interface.php)" and interface.php is include setting.php.

The problem occurs when it call function in interface.php, it cannot use global variable which I declare in setting.php. Yes, I already put global var1,var2,var3; input my function in interface.php. Finally I found that I must put the same into setting.php file as below

setting.php

global $var1,$var2,$var3;

$var1="abc"; and so on.

Which these may help someone who get the same problem like me.