function_exists - PHP code example

The php Function Function Exists

The php function function_exists checks whether a particular function (either built-in or one you've defined yourself) is available for use. Specifically, it takes the name of the function as its only parameter, and it returns true if the function exists, and false otherwise.

Aside from the function_exists() function, there are a number of other functions in PHP that are related to function checking. The class_exists() function is for checking if a specific type of object or class is present, while the method_exists() function is used to check for methods in a particular object or class instance.

Function checks are commonly employed in Model-View-Controller frameworks in order to ensure that a given method is available before calling it. For example, when writing a class that implements an MVC pattern, you would check that the class has the posts and edit methods using the function_exists() function.

Note that the function_exists() function only checks if the specified function actually exists in the current environment; it does not verify that the function will work as it may not be available for use due to a variety of reasons, such as configuration and compiling options. For this reason, it's best to use a debugger integrated with your IDE to help you verify that the functions you are trying to call are available and will actually work.

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function_exists example

    public function owner( $file ) {
        $owneruid = @fileowner( $file );

        if ( ! $owneruid ) {
            return false;
        }

        if ( ! function_exists( 'posix_getpwuid' ) ) {
            return $owneruid;
        }

        $ownerarray = posix_getpwuid( $owneruid );

        if ( ! $ownerarray ) {
            return false;
        }

        return $ownerarray['name'];
    }

// Follow https://no-color.org/         if (isset($_SERVER['NO_COLOR']) || false !== getenv('NO_COLOR')) {
            return false;
        }

        if ('Hyper' === getenv('TERM_PROGRAM')) {
            return true;
        }

        if (\DIRECTORY_SEPARATOR === '\\') {
            return (\function_exists('sapi_windows_vt100_support')
                && sapi_windows_vt100_support(\STDOUT))
                || false !== getenv('ANSICON')
                || 'ON' === getenv('ConEmuANSI')
                || 'xterm' === getenv('TERM');
        }

        if (\function_exists('stream_isatty')) {
            return @stream_isatty(\STDOUT);
        }

        if (\function_exists('posix_isatty')) {

_deprecated_function( __FUNCTION__, '3.4.0', 'WP_Theme::get_allowed_on_site()' );
    return array_map( 'intval', WP_Theme::get_allowed_on_site( $blog_id ) );
}

/** * Deprecated functionality for determining whether a file is deprecated. * * @deprecated 3.5.0 */
function ms_deprecated_blogs_file() {}

if ( ! function_exists( 'install_global_terms' ) ) :
    /** * Install global terms. * * @since 3.0.0 * @since 6.1.0 This function no longer does anything. * @deprecated 6.1.0 */
    function install_global_terms() {
        _deprecated_function( __FUNCTION__, '6.1.0' );
    }
endif;

protected function getConstructor(Definition $definition, bool $required): ?\ReflectionFunctionAbstract
    {
        if ($definition->isSynthetic()) {
            return null;
        }

        if (\is_string($factory = $definition->getFactory())) {
            if (str_starts_with($factory, '@=')) {
                return new \ReflectionFunction(static function D...$args) {});
            }

            if (!\function_exists($factory)) {
                throw new RuntimeException(sprintf('Invalid service "%s": function "%s" does not exist.', $this->currentId, $factory));
            }
            $r = new \ReflectionFunction($factory);
            if (false !== $r->getFileName() && file_exists($r->getFileName())) {
                $this->container->fileExists($r->getFileName());
            }

            return $r;
        }

        if ($factory) {
            [

<?php /** * WordPress database access abstraction class. * * This file is deprecated, use 'wp-includes/class-wpdb.php' instead. * * @deprecated 6.1.0 * @package WordPress */

if ( function_exists( '_deprecated_file' ) ) {
// Note: WPINC may not be defined yet, so 'wp-includes' is used here. _deprecated_file( basename( __FILE__ ), '6.1.0', 'wp-includes/class-wpdb.php' );
}

/** wpdb class */
require_once __DIR__ . '/class-wpdb.php';

private function getRuntimeValue(string $name, SimpleXMLElement $requirement)
    {
        $m = 'check' . str_replace(' ', '', ucwords(str_replace(['_', '.'], ' ', $name)));
        if (method_exists($this, $m)) {
            return $this->$m($requirement);
        }

        if (\extension_loaded($name)) {
            return true;
        }

        if (\function_exists($name)) {
            return true;
        }

        $value = \ini_get($name);
        if ($value !== '' && $value !== false) {
            if ((int) $value === 0 || strtolower($value) === 'off') {
                return false;
            }

            if ((int) $value === 1 || strtolower($value) === 'on') {
                return true;
            }

$force_gzip = ( defined( 'ENFORCE_GZIP' ) && ENFORCE_GZIP );
        $test_str   = '"wpCompressionTest Lorem ipsum dolor sit amet consectetuer mollis sapien urna ut a. Eu nonummy condimentum fringilla tempor pretium platea vel nibh netus Maecenas. Hac molestie amet justo quis pellentesque est ultrices interdum nibh Morbi. Cras mattis pretium Phasellus ante ipsum ipsum ut sociis Suspendisse Lorem. Ante et non molestie. Porta urna Vestibulum egestas id congue nibh eu risus gravida sit. Ac augue auctor Ut et non a elit massa id sodales. Elit eu Nulla at nibh adipiscing mattis lacus mauris at tempus. Netus nibh quis suscipit nec feugiat eget sed lorem et urna. Pellentesque lacus at ut massa consectetuer ligula ut auctor semper Pellentesque. Ut metus massa nibh quam Curabitur molestie nec mauris congue. Volutpat molestie elit justo facilisis neque ac risus Ut nascetur tristique. Vitae sit lorem tellus et quis Phasellus lacus tincidunt nunc Fusce. Pharetra wisi Suspendisse mus sagittis libero lacinia Integer consequat ac Phasellus. Et urna ac cursus tortor aliquam Aliquam amet tellus volutpat Vestibulum. Justo interdum condimentum In augue congue tellus sollicitudin Quisque quis nibh."';

        if ( 1 == $_GET['test'] ) {
            echo $test_str;
            wp_die();
        } elseif ( 2 == $_GET['test'] ) {
            if ( ! isset( $_SERVER['HTTP_ACCEPT_ENCODING'] ) ) {
                wp_die( -1 );
            }

            if ( false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'deflate' ) && function_exists( 'gzdeflate' ) && ! $force_gzip ) {
                header( 'Content-Encoding: deflate' );
                $out = gzdeflate( $test_str, 1 );
            } elseif ( false !== stripos( $_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip' ) && function_exists( 'gzencode' ) ) {
                header( 'Content-Encoding: gzip' );
                $out = gzencode( $test_str, 1 );
            } else {
                wp_die( -1 );
            }

            echo $out;
            wp_die();
        }

foreach ($this->signals as $signal) {
            pcntl_signal($signal, function D) use ($event, $signal) {
                $this->logger?->info('Received signal {signal}.', ['signal' => $signal, 'transport_names' => $event->getWorker()->getMetadata()->getTransportNames()]);

                $event->getWorker()->stop();
            });
        }
    }

    public static function getSubscribedEvents(): array
    {
        if (!\function_exists('pcntl_signal')) {
            return [];
        }

        return [
            WorkerStartedEvent::class => ['onWorkerStarted', 100],
        ];
    }
}

$this->cmd = $cmd;
    }

    public function isGuesserSupported(): bool
    {
        static $supported = null;

        if (null !== $supported) {
            return $supported;
        }

        if ('\\' === \DIRECTORY_SEPARATOR || !\function_exists('passthru') || !\function_exists('escapeshellarg')) {
            return $supported = false;
        }

        ob_start();
        passthru('command -v file', $exitStatus);
        $binPath = trim(ob_get_clean());

        return $supported = 0 === $exitStatus && '' !== $binPath;
    }

    public function guessMimeType(string $path): ?string
    {

private bool $shareOptions;

    /** * Takes an array of options to set the following possible class properties: * * - baseURI * - timeout * - any other request options to use as defaults. */
    public function __construct(App $config, URI $uri, ?ResponseInterface $response = null, array $options = [])
    {
        if (! function_exists('curl_version')) {
            throw HTTPException::forMissingCurl(); // @codeCoverageIgnore         }

        parent::__construct('GET', $uri);

        $this->responseOrig   = $response ?? new Response(config(App::class));
        $this->baseURI        = $uri->useRawQueryString();
        $this->defaultOptions = $options;

        /** @var ConfigCURLRequest|null $configCURLRequest */
        $configCURLRequest  = config(ConfigCURLRequest::class);

function wp_load_image( $file ) {
    _deprecated_function( __FUNCTION__, '3.5.0', 'wp_get_image_editor()' );

    if ( is_numeric( $file ) )
        $file = get_attached_file( $file );

    if ( ! is_file( $file ) ) {
        /* translators: %s: File name. */
        return sprintf( __( 'File “%s” does not exist?' ), $file );
    }

    if ( ! function_exists('imagecreatefromstring') )
        return __('The GD image library is not installed.');

    // Set artificially high because GD uses uncompressed images in memory.     wp_raise_memory_limit( 'image' );

    $image = imagecreatefromstring( file_get_contents( $file ) );

    if ( ! is_gd_image( $image ) ) {
        /* translators: %s: File name. */
        return sprintf( __( 'File “%s” is not an image.' ), $file );
    }

/* * This file is part of the Symfony package. * * (c) Fabien Potencier <fabien@symfony.com> * * For the full copyright and license information, please view the LICENSE * file that was distributed with this source code. */

use Symfony\Polyfill\Intl\Normalizer as p;

if (!function_exists('normalizer_is_normalized')) {
function normalizer_is_normalized(?string $string, ?int $form = p\Normalizer::FORM_C): bool { return p\Normalizer::isNormalized((string) $string, (int) $form); }
}
if (!function_exists('normalizer_normalize')) {
function normalizer_normalize(?string $string, ?int $form = p\Normalizer::FORM_C): string|false { return p\Normalizer::normalize((string) $string, (int) $form); }
}

/** * Alters the UUID service to use the most efficient method available. * * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container * The container builder. */
  public function alter(ContainerBuilder $container) {
    $uuid_service = $container->getDefinition('uuid');
    // Debian/Ubuntu uses the (broken) OSSP extension as their UUID     // implementation. The OSSP implementation is not compatible with the     // PECL functions.     if (function_exists('uuid_create') && !function_exists('uuid_make')) {
      $uuid_service->setClass('Drupal\Component\Uuid\Pecl');
    }
    // Try to use the COM implementation for Windows users.     elseif (function_exists('com_create_guid')) {
      $uuid_service->setClass('Drupal\Component\Uuid\Com');
    }
  }

  /** * Registers services and event subscribers for a site under test. * * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container * The container builder. */

<?php /** * Smarty shared plugin * * @package Smarty * @subpackage PluginsShared */
if (!function_exists('smarty_mb_str_replace')) {

/** * Multibyte string replace * * @param string $search the string to be searched * @param string $replace the replacement string * @param string $subject the source string * @param int &$count number of matches found * * @return string replaced string * @author Rodney Rehm */

return $new;
    }

    public function slug(string $string, string $separator = '-', string $locale = null): AbstractUnicodeString
    {
        $locale ??= $this->defaultLocale;

        $transliterator = [];
        if ($locale && ('de' === $locale || str_starts_with($locale, 'de_'))) {
            // Use the shortcut for German in UnicodeString::ascii() if possible (faster and no requirement on intl)             $transliterator = ['de-ASCII'];
        } elseif (\function_exists('transliterator_transliterate') && $locale) {
            $transliterator = (array) $this->createTransliterator($locale);
        }

        if ($emojiTransliterator = $this->createEmojiTransliterator($locale)) {
            $transliterator[] = $emojiTransliterator;
        }

        if ($this->symbolsMap instanceof \Closure) {
            // If the symbols map is passed as a closure, there is no need to fallback to the parent locale             // as the closure can just provide substitutions for all locales of interest.             $symbolsMap = $this->symbolsMap;