PHP 8 Deprecated Functions: Practical Migration Guide

1. Database & Cryptography Functions: mysql_* & mcrypt_*

Status: Deprecated in PHP 5.5 / 7.1; Removed in PHP 7.0 / 7.2.

Old Code (PHP 5.x):

$res = mysql_query("SELECT * FROM items");
$enc = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, $text, MCRYPT_MODE_ECB);

Modern Replacement (PHP 8.x):

// PDO database query
$stmt = $pdo->query("SELECT * FROM items");
$items = $stmt->fetchAll();

// OpenSSL encryption
$enc = openssl_encrypt($text, 'aes-256-cbc', $key, 0, $iv);

2. Dynamic Functions: create_function() & each()

Status: Deprecated in PHP 7.2; Removed in PHP 8.0.

Old Code:

// create_function replacement
$func = create_function('$a,$b', 'return $a + $b;');

// each() iteration
while (list($key, $val) = each($array)) { ... }

Modern Replacement:

// Anonymous Closure function
$func = fn($a, $b) => $a + $b;

// Standard foreach loop
foreach ($array as $key => $val) { ... }

3. POSIX Regex: split() & ereg_*()

Status: Deprecated in PHP 5.3; Removed in PHP 7.0.

Old Code:

$parts = split(':', $string);
$match = ereg('[a-z]', $string);

Modern Replacement:

$parts = explode(':', $string); // or preg_split()
$match = preg_match('/[a-z]/', $string);

4. Syntax Changes: Curly-Brace String Offsets & money_format()

Status: Curly-brace string access deprecated in PHP 7.4, removed in PHP 8.0. money_format() removed in PHP 7.4 in favor of NumberFormatter.

Old Code:

$char = $str{0}; // Fatal syntax error in PHP 8
$formatted = money_format('%i', $val);

Modern Replacement:

$char = $str[0]; // Square brackets

$fmt = new NumberFormatter('en_US', NumberFormatter::CURRENCY);
$formatted = $fmt->formatCurrency($val, 'USD');

5. Implicit Non-Nullable Internal Parameters

Passing null to non-nullable scalar arguments of core internal functions (e.g. htmlspecialchars(null)) is deprecated in PHP 8.1 and throws deprecation notices or errors.

Related guides: PHP 5.6 to PHP 8 Migration Complete Compatibility Guide and CodeIgniter PHP 8 Migration Common Errors.