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What is the ?? operator in PHP?

PHP & the Web 2 min read Full lesson: Building a PHP Web Form
Short answer

?? returns the left side unless it is null or undefined, in which case it returns the right side. Unlike ?:, it suppresses the undefined-key warning and does not treat 0 or "" as absent.

php
$name = $_POST['name'] ?? 'guest';

#The three lookalikes

php
$a = $value ?? 'default';          // null coalescing
$b = $value ?: 'default';          // short ternary — checks falsiness
$c = isset($value) ? $value : 'default';   // the long form ?? replaces

The difference shows up on falsy-but-present values:

php
$count = 0;

$count ?? 5;      // 0  — it is set, so it wins
$count ?: 5;      // 5  — 0 is falsy, so the default wins

For a quantity, a page number or a score, ?: silently replaces a legitimate zero. ?? does not.

?: also emits a warning if the variable does not exist. ?? never does — that is its main job.

#Chaining

php
$value = $a ?? $b ?? $c ?? 'fallback';

Evaluation is left to right and stops at the first non-null.

#Assignment form

php
$config['timeout'] ??= 30;      // set only if missing or null

#Nullsafe method calls

Related, and often confused with it:

php
$country = $user?->address?->country;

?-> returns null instead of throwing when the left side is null. Useful for optional relations — but be careful not to use it to paper over a null that should never have happened.

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