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<New Global ConstantsDeprecated Features>
^Migrating from PHP 8.3.x to PHP 8.4.xLast updated: Mon, 26 Oct 2026

Backward Incompatible Changes

Although not explicitly stated in this section, every new function, class, interface, enum, or constant may cause a redeclaration Error to be thrown.

PHP Core

exit() behavioral change

The exit() (and die()) language constructs now behave more like a function. This means that they can now be passed like callables, are affected by the strict_types declare statement, and now perform the usual type coercions instead of casting any non-integer value to a string.

As such, passing invalid types to exit() and die() now consistently result in a TypeError being thrown.

Recursion during comparison

Encountering recursion during comparison now results in an Error exception instead of a E_ERROR fatal error.

Indirect Modification of readonly Properties

Indirect modification of readonly properties within __clone() is no longer allowed, e.g. $ref = &$this->readonly. This was already forbidden for readonly initialization, and was an oversight in the "readonly reinitialization during cloning" implementation.

Type Change of Constants

The PHP_DEBUG and PHP_ZTS constants are now of type bool. Previously they were of type int.

Temporary Filename Length

The name of uploaded files and files created by the tempnam() function are now 13 bytes longer. The total length is still platform-dependent.

Removal of E_STRICT error level

The E_STRICT error level has been removed, as it was no longer in use within the PHP engine. The E_STRICT constant has been deprecated.

Extension Class Constants which are now Typed

The following extension class constants now declare a type on their constants:

Resource to Object Migration

Several resources have been migrated to objects. Return value checks using is_resource() should be replaced with checks for false, unless specified otherwise.

DBA

The DBA functions now accept and return Dba\Connection objects instead of dba_connection resources.

ODBC

The ODBC functions now accept and return Odbc\Result objects instead of odbc_result resources.

The ODBC functions now accept and return Odbc\Connection objects instead of odbc_connection resources.

SOAP

The SoapClient::$httpurl property is now a Soap\Url object rather than a soap_url resource. Checks using is_resource() (i.e. is_resource($client->httpurl)) should be replaced with checks for null (i.e. $client->httpurl !== null).

The SoapClient::$sdl property is now a Soap\Sdl object rather than a soap_sdl resource. Checks using is_resource() (i.e. is_resource($client->sdl)) should be replaced with checks for null (i.e. $client->sdl !== null).

New warnings and exceptions

New warnings and exceptions have been added which are triggered on programming errors, i.e. invalid values provided as arguments.

Curl

curl_multi_select() now throws a ValueError if the timeout parameter is less than 0 or greater than PHP_INT_MAX.

Gd

imagejpeg(), imagewebp(), imagepng(), imageavif() now throw a ValueError when an invalid quality is passed.

imageavif() will now throw a ValueError if an invalid speed parameter value is passed.

imagescale() will now throw a ValueError if the width or height parameters underflows/overflows.

imagescale() will now throw a ValueError if an invalid mode parameter value is passed.

imagefilter() will now throw a ValueError with the IMG_FILTER_SCATTER filter if the sub or plus parameters underflows/overflows.

Gettext

bind_textdomain_codeset(), textdomain(), d*gettext now throw a ValueError if domain is the empty string.

Intl

resourcebundle_get(), ResourceBundle::get(), and accessing offsets on a ResourceBundle object now throw:

IntlDateFormatter::__construct() throws a ValueError if the locale is invalid.

NumberFormatter::__construct() throws a ValueError if the locale is invalid.

MBString

mb_encode_numericentity() and mb_decode_numericentity() now check that the map is only composed of ints, if not a ValueError is now thrown.

mb_http_input() now always throw a ValueError if type is invalid.

mb_http_output() now check that the encoding does not contain any null bytes, if it does a ValueError is now thrown.

ODBC

odbc_fetch_row() returns false when row is less than or equal to 0. A warning is now emitted in this case.

PCNTL

The pcntl_sigprocmask(), pcntl_sigwaitinfo(), and pcntl_sigtimedwait() functions now throw:

The pcntl_sigprocmask() function now throws a ValueError if the mode is not one of SIG_BLOCK, SIG_UNBLOCK, or SIG_SETMASK.

The pcntl_sigtimedwait() function now throw:

  • A ValueError if seconds is less than 0
  • A ValueError if nanoseconds is less than 0 or greater than 1e9
  • A ValueError if both seconds and nanoseconds are 0

Session

Setting a non-positive value for session.gc_divisor or a negative value for session.gc_probability now emits a warning.

SimpleXML

Calling simplexml_import_dom() with a non-XML object now throws a TypeError instead of a ValueError.

Standard

The round() function now validates the value of the mode and throw a ValueError for invalid modes. Previously, invalid modes would have been interpreted as PHP_ROUND_HALF_UP.

The str_getcsv() now throws ValueErrors when the separator and enclosure arguments are not one byte long, or if the escape argument is not one byte long nor the empty string. This aligns the behaviour to be identical to the one of fputcsv() and fgetcsv().

The php_uname() function now throws a ValueError if the mode is invalid.

The "allowed_classes" option for unserialize() now throws TypeError and ValueError if it is neither an array of class names nor a bool.

XMLReader

Passing an invalid character encoding to XMLReader::open() or XMLReader::XML() now throws a ValueError.

Passing a string containing null bytes previously emitted a warning and now throws a ValueError.

XMLWriter

Passing a string containing null bytes previously emitted a warning and now throws a ValueError.

XSL

XSLTProcessor::setParameter() will now throw a ValueError when its arguments contain null bytes. This never actually worked correctly in the first place, which is why it throws an exception now.

Calling XSLTProcessor::importStyleSheet() with a non-XML object now throws a TypeError instead of a ValueError.

Failure to call a PHP function callback during evaluation now throws instead of emitting a warning.

Date

number symbols in relative formats once again accept multiple signs, e.g. +-2.

DOM

Some DOM methods previously returned false or a DOMException with code DOM_PHP_ERR if a new node could not be allocated. They now consistently throw a DOMException with code DOM_INVALID_STATE_ERR. This situation is extremely unlikely and the probability of being affected is low. As a result DOMImplementation::createDocument() now has a tentative return type of DOMDocument instead of DOMDocument|false.

Previously, DOMXPath objects could be cloned, but resulted in an unusable object. This is no longer possible, and cloning a DOMXPath object now throws an Error.

The DOMImplementation::getFeature() method has been removed.

GMP

The GMP class is now final and cannot be extended anymore.

MBString

As of PHP 8.3.2, on invalid strings (those with encoding errors), mb_substr() and mb_strstr() interpret character indices in the same manner as most other mbstring functions. This means that character indices returned by mb_strpos() can be passed to mb_substr().

For SJIS-mac (MacJapanese) strings, those character indices refer to the indices of the Unicode codepoints which are produced when the string is converted to Unicode, which differ from the character indices for the SJIS-mac characters that convert to a sequence of several codepoints.

MySQLi

The unused and undocumented constant MYSQLI_SET_CHARSET_DIR has been removed.

The MYSQLI_STMT_ATTR_PREFETCH_ROWS constant has been removed. The feature is unavailable with mysqlnd.

The MYSQLI_CURSOR_TYPE_FOR_UPDATE and MYSQLI_CURSOR_TYPE_SCROLLABLE constants have been removed. This functionality was never implemented, neither with mysqlnd nor with libmysql.

The unused MYSQLI_TYPE_INTERVAL constant, which is currently a stub and an alias for MYSQLI_TYPE_ENUM, has been removed.

MySQLnd

The error code reported for MySQL server wait timeouts has been changed from 2006 to 4031 for MySQL server versions 8.0.24 and above.

Opcache

The maximum value of the opcache.interned_strings_buffer setting on 64bit architectures is now 32767. Previously it was 4095.

JIT

The default configuration values for the JIT changed from opcache.jit=tracing and opcache.jit_buffer_size=0 to opcache.jit=disable and opcache.jit_buffer_size=64M, respectively.

This does not affect the default observable behavior, as the JIT is still disabled by default. However, it is now disabled through the opcache.jit setting, rather than opcache.jit_buffer_size. This may affect users who previously enabled JIT through opcache.jit_buffer_size exclusively, without also specifying a JIT mode using opcache.jit. To enable JIT compilation, set the opcache.jit config value accordingly.

If JIT compilation is enabled, PHP will now exit with a fatal error on startup if the initialization of the JIT compiler failed for any reason.

PCNTL

The pcntl_sigprocmask(), pcntl_sigwaitinfo(), and pcntl_sigtimedwait() functions now always return false on failure. In some case previously it could return the value -1.

PCRE

The bundled pcre2lib has been updated to version 10.44. As a consequence, this means {,3} is now recognized as a quantifier instead of as text. Furthermore, the meaning of some character classes in UCP mode has changed. Consult the » PCRE2 Changelog for a full changelog.

PDO_DBLIB

The Pdo\Dblib::ATTR_STRINGIFY_UNIQUEIDENTIFIER and Pdo\Dblib::ATTR_DATETIME_CONVERT attributes now act as boolean attributes instead of integer attributes. Thus setting the attribute via PDO::setAttribute() and retrieving it via PDO::getAttribute() expects and or return a bool.

PDO_FIREBIRD

The PDO::ATTR_AUTOCOMMIT attribute now act as boolean attributes instead of integer attributes. Thus setting the attribute via PDO::setAttribute() and retrieving it via PDO::getAttribute() expects and or return a bool.

The extension now exposes some Firebird C++ APIs, therefore building this extension now requires a C++ compiler. Moreover, the extension must now be compiled against fbclient 3.0 or higher.

PDO_MYSQL

The PDO::ATTR_AUTOCOMMIT, PDO::ATTR_EMULATE_PREPARES, and PDO::MYSQL_ATTR_DIRECT_QUERY attributes now act as boolean attributes instead of integer attributes. Thus setting the attribute via PDO::setAttribute() and retrieving it via PDO::getAttribute() expects and or return a bool.

PDO_PGSQL

The DSN's credentials, when set, are given priority over their PDO constructor counterparts, being closer to the documentation states.

SimpleXML

SimpleXMLElement is not only a representation of an XML element, but it is also a RecursiveIterator. Prior to PHP 8.4.0, some of its methods (e.g. SimpleXMLElement::asXML() or SimpleXMLElement::getName()) and casting such instances to string would implicitly reset the iterator.

This could cause unexpected infinite loops as the iterator was rewound. For example: 

<?php

$xmlString = "<root><a><b>1</b><b>2</b><b>3</b></a></root>";
$xml = simplexml_load_string($xmlString);

$nodes = $xml->a->b;
foreach ($nodes as $nodeData) {
    echo "nodeData: " . $nodeData . "\n";

    $xml = $nodes->asXml();
}

would result in an infinite loop. 

nodeData: 1
nodeData: 2
nodeData: 2
nodeData: 2
nodeData: 2
nodeData: 2
nodeData: 2
// ...

However, this behavior has now been corrected, and a SimpleXMLElement will no longer implicitly reset the iterator data, unless explicitly rewound. Meaning the previous example would now result in: 

nodeData: 1
nodeData: 2
nodeData: 3

SOAP

SoapClient::$typemap is now an array rather than a resource. Checks using is_resource() (i.e. is_resource($client->typemap)) should be replaced with checks for null (i.e. $client->typemap !== null).

The SOAP extension gained an optional dependency on the session extension. If PHP is built without the session extension and with the --enable-rtld-now configure flag enabled, startup errors will now occur if the SOAP extension is also used. To solve this either don't use rtld-now or load the session extension.

Standard

When using strcspn() with characters being the empty string, the length of the string is now returned instead of incorrectly stopping at the first null byte.

http_build_query() now correctly handles backed enums.

stream_bucket_make_writeable() and stream_bucket_new() will now return a StreamBucket instance instead of an instance of stdClass.

Tidy

Failures in the constructor now throw exceptions rather than emitting warnings and having a broken object.

XML

The xml_set_*_handler functions now declare and check for an effective signature of callable|string|null for the handler parameters. Moreover, values of type string that correspond to method names, of object set with xml_set_object() are now checked to see if the method exists on the class of the previously passed object. This means that xml_set_object() must now always be called prior to setting method names as callables. Passing an empty string to disable the handler is still allowed, but deprecated.

However, as xml_set_object() and passing non-callable strings is deprecated. It is recommended to change such instances with a callable referring to the method directly.


<New Global ConstantsDeprecated Features>
^Migrating from PHP 8.3.x to PHP 8.4.xLast updated: Mon, 26 Oct 2026