include.class.PHP
<?PHP
class IncludeTest {
}
?>
test.PHP
<?PHP
//报错
//Fatal error: Cannot redeclare class IncludeTest in D:\myPHP\research\include_test\include.class.PHP on line 3
//require('include.class.PHP');
//require('include.class.PHP');
//报错
//Fatal error: Cannot redeclare class IncludeTest in D:\myPHP\research\include_test\include.class.PHP on line 3
//require_once('include.class.PHP');
//require('include.class.PHP');
//不报错
//require('include.class.PHP');
//require_once('include.class.PHP');
//不报错
require_once('include.class.PHP');
require_once('include.class.PHP');
//总结,两次加载同一文件,只要后面一个用require_once,则不报错。
?>
还有一种情况,就是在多个地方加载了同一个类,但是即使用了incluce_once或require_once仍然会报错(暂时不知道是什么原因导致的),此时有一种办法可以解决,那就是在加载之前用class_exists判断一下,且第二参数用false,这样可以提高性能,用class_exists判断一下后,就不会报Cann't redeclare class的错误了。
例如if (!class_exists('Smarty', false)) include_once('/path/to/Smarty.class.PHP');
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转载于:https://www.cnblogs.com/itcx/p/3890075.html