How to determine whether a class exists in php

In PHP, you can use the class_exists() function to determine whether the specified class exists. The function of this function is to check whether the class has been defined. The syntax is "class_exists('class name')"; if the specified class If it has been defined (exists), it returns true, otherwise it returns false.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

In php, you can use the class_exists() function To determine whether the specified class exists.

The class_exists() function can check whether the specified class has been defined.

Syntax:

class_exists(string $class, bool $autoload = true): bool

• class: class name. Name matching is case-insensitive.

• autoload: Whether to call __autoload by default.

Return value:

• If the class pointed to by class has been defined, this function returns true , otherwise return false.

Example 1: Check whether class HelloWorld has been defined

<?php
   if (class_exists(&#39;HelloWorld&#39;)) {
      $helloworld = new HelloWorld();
   }
?>

class_exists() will try to call _autoload by default, if you don’t want class_exists() When calling _autoload, you can set the autoload parameter to FALSE.

Example 2: autoload parameter example

<?php
function __autoload($class)
{
    include($class . &#39;.php&#39;);

    // Check to see if the include declared the class
    if (!class_exists($class, false)) {
        trigger_error("Unable to load class: $class", E_USER_WARNING);
    }
}

if (class_exists(&#39;MyClass&#39;)) {
    $myclass = new MyClass();
}

?>

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