Can you explain why buffering is useful?

Question

PHP

function display(){/* работа шаблонизатора, замена меток */}
ob_start(display);
  require 'template/index.html';
ob_end_flush();

I saw this code, and I can't understand how this ob_start is useful.
In the documentation, as elsewhere, they simply write:
This function enables output buffering. If output buffering is active, script output is not sent (except headers), but stored in an internal buffer.

Answer 1

Once upon a time, php did not use a buffer and sent everything to the client at once.
Roughly like this

<?php

for ($i = 1; $i <= 100; $i++) {
    echo $i;
    ob_flush();
    flush();

    usleep(300000);
}
ob_end_flush();

The buffer is now enabled by default.
And it looks like this. ( Sergey Protko already said this )

<?php

$buffer = '';
for ($i = 1; $i <= 100; $i++) {
    $buffer .= $i;
    if (strlen($buffer) > 50) {
        echo $buffer;
        $buffer = '';
    }
}
echo $buffer;

But apart from the headers already mentioned...
The buffer can be controlled.
For example. We have an error in the included template.
Without a buffer, puff will gladly give it to the client and die halfway through.
With a buffer, we can "ignore" it or change the contents altogether.
As a result, on the page where we have the menu, it will not show off "PHP Notice ....",
but the human text "An error has occurred" or even an empty space.

<?php

error_reporting(E_ALL);
ini_set('display_errors', 1);

$buffer = '';

function handler($ouputBuffer) {
    global $buffer;
    $buffer = $ouputBuffer;
}

ob_start('handler');
$ChuckNorris = 5 / 0;
ob_end_flush();

// Клиенту не полетит E_WARNING
echo "E_WARNING"; 

echo "<pre>";
var_dump($buffer);
echo "</pre>";
exit("File: " . __FILE__ . " Line: " . __LINE__);

In any case, this is a useful thing and you need to understand it at least a little, but understand it.

Answer 2

Ensure that the HTTP headers are sent before the content.

Answer 3

You can intercept and modify the output of a script written by another developer in order to perform additional manipulations on this output or completely clear it.