Consider the following snippet:
<?php
error_reporting(E_ALL);
function bar()
{
	global $foo;
}
echo $foo; // prints a warning
bar();
echo $foo; // no warning
?>
The first echo $foo prints a warning saying "Undefined variable: $foo in ..."
The second echo $foo doesn't output a warning.

The following snippet is even more strange:
<?php
error_reporting(E_ALL);
function bar()
{
	global $foo;
	return isset($foo)?1:0; 
}

echo isset($foo)?1:0; // prints 0 (correct)
echo $foo;            // prints a warning (correct)
echo bar();           // prints 0 (correct)
echo isset($foo)?1:0; // prints 0 (correct)
echo $foo;            // doesn't print a warning (not correct)
?>
So, isset() says $foo doesn't exists (and so does is_null()). If it doesn't exist, echo'ing $foo should produce an error with E_ALL, but it doesn't.

I don't know whether this is a bug or undocumented behaviour. If it's not a bug, it's a very strange and confusing behaviour.


Tested with 4.0.6, 4.0.7RC3, and 4.2.0-dev from 200110160600, on Windows 2000.