The newly added NULL coalescing operator (??) in PHP 7 is a shortcut for performing the ternary operation detected by isset().

The NULL coalescing operator will determine whether the variable exists and the value is not NULL. If so, it will return its own value, otherwise it will return its second operand.

In the past we wrote the ternary operator like this:

$site = isset($_GET['site']) ? $_GET['site'] : 'php中文網(wǎng)';

Now we can write it directly like this:

$site = $_GET['site'] ?? 'php中文網(wǎng)';

Example

<?php
// 獲取 $_GET['site'] 的值，如果不存在返回 'php中文網(wǎng)'
$site = $_GET['site'] ?? 'php中文網(wǎng)';

print($site);
echo "<br/>"; // PHP_EOL 為換行符


// 以上代碼等價(jià)于
$site = isset($_GET['site']) ? $_GET['site'] : 'php中文網(wǎng)';

print($site);
echo "<br/>";
// ?? 鏈
$site = $_GET['site'] ?? $_POST['site'] ?? 'php中文網(wǎng)';

print($site);
?>

The execution output of the above program is :

php中文網(wǎng)
php中文網(wǎng)
php中文網(wǎng)