Example of PHP nested output caching

The output cache of PHP can be nested. You can output nesting levels with Ob_get_level ().

The test found that the output was different between the CLI and the browser (PHP5.4).

The Ob_level1.png manual describes the following:

Ob_get_level () would always return 0 inside a destructor.
This happens because the garbage collection for output buffers has already do before the destructor is called

It's also easy to get the right output:

Ob_end_clean ();
Echo Ob_get_level (); 0

Back to the point:

Ob_end_clean ();

Ob_start ();
Echo ' PHP1 ';//This does not output in the page
$a = Ob_get_level ();
$b = ob_get_contents ()//Get cache result, assign variable
Ob_clean ();

Ob_start ();
Echo ' PHP2 ';//This does not output in the page
$c = Ob_get_level ();
$d = ob_get_contents ()//Get cache result, assign variable
Ob_clean ();

Ob_start ();
Echo ' php3 ';//This does not output in the page
$e = Ob_get_level ();
$f = ob_get_contents ()//Get cache result, assign variable
Ob_clean ();

echo ' Level: '. $a. ', ouput: '. $b. ' <br> ';
echo ' Level: '. $c. ', ouput: '. $d. ' <br> ';
echo ' Level: '. $e. ', ouput: '. $f. ' <br> ';

The results are as follows:

Level:1,ouput:php1
Level:2,ouput:php2
Level:3,ouput:php3

Of course, when you turn off a certain level of buffering, test as follows:
Ob_end_clean ();

Ob_start ();
Echo ' PHP1 ';
$a = Ob_get_level ();
$b = Ob_get_contents ();
Ob_clean ();

Ob_start ();
Echo ' PhP2 ';
$c = Ob_get_level ();
$d = Ob_get_contents ();
Ob_end_clean (); Empty the cache and close the cache

Ob_start ();
Echo ' php3 ';
$e = Ob_get_level ();
$f = Ob_get_contents ();
Ob_clean ();

echo ' Level: '. $a. ', ouput: '. $b. ' <br> ';
echo ' Level: '. $c. ', ouput: '. $d. ' <br> ';
echo ' Level: '. $e. ', ouput: '. $f. ' <br> ';

The results are as follows:

Level:1,ouput:php1
Level:2,ouput:php2
Level:2,ouput:php3