class_exists

If you are using aliasing to import namespaced classes, take care that class_exists will not work using the short, aliased class name - apparently whenever a class name is used as string, only the full-namespace version can be useduse a\namespaced\classname as coolclass;class_exists( 'coolclass' ) => false

Note: class_exists() check only classes! <?phpinterface DemoInterface {};var_dump(class_exists('DemoInterface')); // falsetrait DemoTrait {};var_dump(class_exists('DemoTrait')); // falseclass DemoClass {};var_dump(class_exists('DemoClass')); // true?>Common function:<?php/**  * Checks if the class/trait/interface has been defined.  *  * @param string $name The case-insensitive name of class/trait/interface  * @param bool $autoload Whether to call spl_autoload()  * @return bool  */function structure_exists(string $name, bool $autoload = true): bool{       return class_exists($name, $autoload)              || interface_exists($name, $autoload)              || trait_exists($name, $autoload);}?>

Beware: class_exists is case-INsensitive, as is class instantiation.php > var_dump(class_exists("DomNode"));bool(true)php > var_dump(class_exists("DOMNode"));bool(true)php > var_dump(class_exists("DOMNodE"));bool(true)php > $x = new DOMNOdE();php > var_dump(get_class($x));string(7) "DOMNode"(tested with PHP 5.5.10 on Linux)This can cause some headaches in correlating class names to file names, especially on a case-sensitive file system.

If you recursively load several classes inside an autoload function (or mix manual loading and autoloading), be aware that class_exists() (as well as get_declared_classes()) does not know about classes previously loaded during the *current* autoload invocation.Apparently, the internal list of declared classes is only updated after the autoload function is completed.

Hi guys!Be careful  and don't forget about second boolean argument $autoload (TRUE by default) when check exists class after spl_autoload_register. Propose short examplefile second.php<?phpclass Second {}?>file index.php<?phpclass First{    function first($class, $bool) {        spl_autoload_register( function($class) {            require strtolower($class) . '.php';        });        echo class_exists($class, $bool)?'Exist!!!!':'Not exist!';    }}new First($class = 'Second', $bool = true); //Exist!!!!new First($class = 'Second', $bool = false); //Not exist!?>Because __autoload executing much earlier than boolean returned, imho..

Beware that `\class_exists()` returns `true` for enums.<?phpenum Test: int{    case One = 1;    case Two = 2;}\var_dump(\class_exists(Test::class)); // bool(true)?>Having this in mind, the correct check for a class existence is:<?phpfunction is_class_exist(string $class): bool{    return \class_exists($class) && !\enum_exists($class);}?>

[ >= PHP 5.3]If you are checking if a class exists that is in a specific namespace then you have to pass in the full path to the class:echo (class_exists("com::richardsumilang::common::MyClass")) ? "Yes" : "No";

If you have a directory of classes you want to create. (Modules in my instance)... you can do it like that

<?php
if (is_dir($this->MODULE_PATH) && $dh = opendir($this->MODULE_PATH)) {
   while (($file = readdir($dh)) !== false) {        
      if (preg_match("/(Mod[a-zA-Z0-9]+).php/", $file, $matches)>0) {                
         // include and create the class               
         require_once($this->MODULE_PATH."/".$file);
         $modules[] = new $matches[1]();
      }                
   }
} else {
   exit;
}
?>

//---
Here the rule is that all modules are on the form
ModModulename.php and that the class has the same name as the file.
The $modules array has all the classes initialized after this code

I'm running PHP 5.3.4 on Windows 7 and had some difficulty autoloading classes using class_exists(). In my case, when I checked for the class and it didn't exist, class_exists automatically threw a system Exception. I was also throwing my own exception resulting in an uncaught exception.<?php/** * Set my include path here */$include_path = array( '/include/this/dir', '/include/this/one/too' );set_include_path( $include_path );spl_autoload_register();/** * Assuming I have my own custom exception handler (MyException) let's * try to see if a file exists. */try {    if( ! file_exists( 'myfile.php' ) ) {        throw new MyException('Doh!');    }    include( 'myfile.php' );}catch( MyException $e ) {    echo $e->getMessage();}/** * The above code either includes myfile.php or throws the new MyException * as expected. No problem right? The same should be true of class_exists(),  * right? So then... */$classname = 'NonExistentClass';try {    if( ! class_exists( $classname ) ) {        throw new MyException('Double Doh!');    }    $var = new $classname();}catch( MyException $e ) {    echo $e->getMessage();}/*** Should throw a new instance of MyException. But instead I get an* uncaught LogicException blah blah blah for the default Exception* class AND MyException. I only catch MyException so we've got on* uncaught resulting in the dreaded LogicException error.*/?>By registering an additional autoload handler function that did nothing, I was able to stop throwing the extra Exception and only throw my own.<?php/** * Set my include path here */$include_path = array( '/include/this/dir', '/include/this/one/too' );set_include_path( $include_path );spl_autoload_register();spl_autoload_register( 'myAutoLoad' ); // Add these two and no worries...function myAutoLoad() {}/** * By registering the additional custom autoload function that does nothing * class_exists() returns only boolean and does NOT throw an uncaught Exception */?>Found this buried in some search results. I don't remember the page URL but if it would have been here it might have saved me some time!