What are common errors when upgrading from PHP 4 to PHP 5 or 7?

Common errors when upgrading from PHP 4 to PHP 5 or 7 include deprecated functions, changes in syntax, and stricter error handling. To solve these issues, update deprecated functions to their newer equivalents, adjust syntax to comply with the new standards, and handle errors more rigorously. 

// Deprecated function in PHP 4: 
// mysql_connect($host, $user, $password);

// Updated function in PHP 5 or 7:
// mysqli_connect($host, $user, $password);

// Deprecated syntax in PHP 4:
// $variable = "Hello World";

// Updated syntax in PHP 5 or 7:
// $variable = 'Hello World';

// Stricter error handling in PHP 5 or 7:
// Use try-catch blocks to handle exceptions more effectively

Keywords

backward compatibility deprecated functions syntax changes PHP 4 to PHP 5 migration PHP 5 to PHP 7 migration

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