Difference between ob_clean and ob_flush?

Question

What's the difference between ob_clean() and ob_flush()?

Also what's the difference between ob_end_clean() and ob_end_flush()? I know ob_get_clean() and ob_get_flush() both get the contents and end output buffering.

Answer 1

the *_clean variants just empty the buffer, whereas *_flush functions print what is in the buffer (send the contents to the output buffer).

Example:

ob_start(); print "foo";      // This never prints because ob_end_clean just empties ob_end_clean();   //    the buffer and never prints or returns anything.  ob_start(); print "bar";      // This IS printed, but just not right here. ob_end_flush();   // It's printed here, because ob_end_flush "prints" what's in                   // the buffer, rather than returning it                   //     (unlike the ob_get_* functions) 

Answer 2

The key difference is *_clean() discards changes and *_flush() outputs to the browser.

Usage of ob_end_clean()

it is mostly used when you want to have a chunk of html and do not want to output to the browser right away but may be used in future.

Eg.

ob_start() echo "<some html chunk>"; $htmlIntermediateData = ob_get_contents(); ob_end_clean();  {{some more business logic}}  ob_start(); echo "<some html chunk>"; $someMoreCode = ob_get_content(); ob_end_clean();  renderTogether($htmlIntermediateCode, $someMoreCode); 

where as ob_end_flush() will render twice, once for each.