Backward Incompatible Changes

Although most existing PHP 5 code should work without changes, please take note of some backward incompatible changes:

• Safe mode is no longer supported. Any applications that rely on safe mode may need adjustment, in terms of security.
• Magic quotes has been removed. Applications relying on this feature may need to be updated, to avoid security issues. get_magic_quotes_gpc() and get_magic_quotes_runtime() now always return FALSE. set_magic_quotes_runtime() raises an E_CORE_ERROR level error.
• The register_globals and register_long_arrays php.ini directives have been removed.
• Call-time pass by reference has been removed.
• The break and continue statements no longer accept variable arguments (e.g., break 1 + foo() * $bar;). Static arguments still work, such as break 2;. As a side effect of this change break 0; and continue 0; are no longer allowed.
• In the date and time extension, the timezone can no longer be set using the TZ environment variable. Instead you have to specify a timezone using the date.timezone php.ini option or date_default_timezone_set() function. PHP will no longer attempt to guess the timezone, and will instead fall back to "UTC" and issue a E_WARNING.
• Non-numeric string offsets - e.g. $a['foo'] where $a is a string - now return false on isset() and true on empty(), and produce a E_WARNING if you try to use them. Offsets of types double, bool and null produce a E_NOTICE. Numeric strings (e.g. $a['2']) still work as before. Note that offsets like '12.3' and '5 foobar' are considered non-numeric and produce a E_WARNING, but are converted to 12 and 5 respectively, for backward compatibility reasons. Note: Following code returns different result. $str='abc';var_dump(isset($str['x'])); // false for PHP 5.4 or later, but true for 5.3 or less
• Converting an array to a string will now generate an E_NOTICE level error, but the result of the cast will still be the string "Array".
• Turning NULL, FALSE, or an empty string into an object by adding a property will now emit an E_WARNING level error, instead of E_STRICT.
• Parameter names that shadow super globals now cause a fatal error. This prohibits code like function foo($_GET, $_POST) {}.
• The Salsa10 and Salsa20 hash algorithms have been removed.
• array_combine() now returns array() instead of FALSE when two empty arrays are provided as parameters.
• If you use htmlentities() with asian character sets, it works like htmlspecialchars() - this has always been the case in previous versions of PHP, but now an E_STRICT level error is emitted.

The following keywords are now reserved, and may not be used as names by functions, classes, etc.

• trait
• callable
• insteadof

The following functions have been removed from PHP:

• define_syslog_variables()
• import_request_variables()
• session_is_registered(), session_register() and session_unregister().
• The aliases mysqli_bind_param(), mysqli_bind_result(), mysqli_client_encoding(), mysqli_fetch(), mysqli_param_count(), mysqli_get_metadata(), mysqli_send_long_data(), mysqli::client_encoding() and mysqli_stmt::stmt().