PHP ?? (Null Coalescing) and ?: (Ternary Shorthand)

?: — Ternary operator (shorthand)

Available since PHP 5.3 (full ternary existed earlier; shorthand since 5.3), return the left value if it is truthy, otherwise return the right value.

Syntax: expr1 ?: expr2

Example:

$name = $_GET['name'] ?: 'Guest';
	
// Equivalent to
$name = $_GET['name'] ? $_GET['name'] : 'Guest';

// Truthy Examples
if (true);         // true → truthy
if (1);            // integer non-zero → truthy
if (3.14);         // float non-zero → truthy
if ('hello');      // non-empty string → truthy
if ([1,2,3]);      // non-empty array → truthy
if (new stdClass); // object → truthy

// Falsy Examples
if (false);    // false → falsy
if (0);        // integer zero → falsy
if (0.0);      // float zero → falsy
if ('0');      // string "0" → falsy
if ('');       // empty string → falsy
if ([]);       // empty array → falsy
if (null);     // null → falsy

Important: Triggers a notice if the left variable is undefined.

?? — Null coalescing operator

Available since PHP 7.0, return the left value if it exists and is not null, otherwise return the right value.

Syntax: expr1 ?? expr2

Example:

$name = $_GET['name'] ?? 'Guest';

// Equivalent to
$name = isset($_GET['name']) ? $_GET['name'] : 'Guest';

Key differences vs ?:

• Does not raise notices for undefined variables
• Checks only for null, not truthiness

Practical Comparison & Chaining

$val1 = 0;
echo $val1 ?: 'fallback'; // outputs 'fallback'
echo $val1 ?? 'fallback'; // outputs 0

// Chaining ??
$lang = $_GET['lang'] ?? $_SESSION['lang'] ?? 'en';

Summary

• Use ?: when you want truthy/falsy behavior
• Use ?? when you want safe defaults without notices