Although most existing PHP 5 code should work without changes, please take note of some backward incompatible changes:
Support for Windows XP and 2003 has been dropped. Windows builds of PHP now require Windows Vista or newer.
All case insensitive matching for function, class and constant names is now performed in a locale independent manner according to ASCII rules. This improves support for languages using the Latin alphabet with unusual collating rules, such as Turkish and Azeri.
This may cause issues for code that uses case insensitive matches for non-ASCII characters in multibyte character sets (including UTF-8), such as accented characters in many European languages. If you have a non-English, non-ASCII code base, then you will need to test that you are not inadvertently relying on this behaviour before deploying PHP 5.5 to production systems.
Changes were made to pack() and unpack() to make them more compatible with Perl:
Writing backward compatible code that uses the "a" format code with unpack() requires the use of version_compare(), due to the backward compatibility break.
For example:
<?php
// Old code:
$data = unpack('a5', $packed);
// New code:
if (version_compare(PHP_VERSION, '5.5.0-dev', '>=')) {
$data = unpack('Z5', $packed);
} else {
$data = unpack('a5', $packed);
}
?>
When the value passed to json_encode() triggers a JSON encoding error,
FALSE is returned instead of partial output,
unless options contains JSON_PARTIAL_OUTPUT_ON_ERROR.
See json_last_error() for the full list of reasons that can cause JSON encoding to fail.
One of the potential failure reasons is that value contains strings containing invalid UTF-8.
self, parent and static are now always case insensitive
Prior to PHP 5.5, cases existed where the
self,
parent, and
static
keywords were treated in a case sensitive fashion. These have now been
resolved, and these keywords are always handled case insensitively:
SELF::CONSTANT is now treated identically to
self::CONSTANT.
The GUIDs that previously resulted in PHP outputting various logos have been removed. This includes the removal of the functions to return those GUIDs. The removed functions are:
Extension authors should note that the zend_execute()
function can no longer be overridden, and that numerous changes have been
made to the execute_data struct and related function
and method handling opcodes.
Most extension authors are unlikely to be affected, but those writing extensions that hook deeply into the Zend Engine should read the notes on these changes.