PHP检测类是否存在方法是什么?
在PHP中可以使用“class_exists()”函数检测类是否存,该函数的作用是检查类是否已定义,其用法为“class_exists($class_name)”,其参数“$class_name”代表要检测的类名。
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示例代码
<?php // 使用前检查类是否存在 if (class_exists('MyClass')) { $myclass = new MyClass(); } ?>
<?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. */ ?>
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