Ob_start ([string output_callback])-Open output buffer
All output information is not sent directly to the browser, but is stored in the output buffer, which is used to process output information.
Ob_end_flush-End (send) the contents of the output buffer, turn off the output buffer
Using the output control function allows you to give free rein to the data in your script, which is useful when we want to output it before the header.
The code is as follows: <?php
The personal use of OB is mostly when generating static HTML, when a page does not refresh, and when other users browse the page again, the program will no longer invoke PHP and related database tutorials. It is good practice to use OB to generate HTML at this time.