PHP eval() function, phpeval function_PHP tutorial

PHP eval() function, phpeval function

Definition and usage

The eval() function evaluates strings according to PHP code.

The string must be valid PHP code and must end with a semicolon.

If no return statement is called in the code string, NULL is returned. If there are parsing errors in the code, the eval() function returns false.

Grammar

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eval(phpcode)

　

参数	描述
phpcode	必需。规定要计算的 PHP 代码。

Tips and Notes

Note: The return statement immediately terminates the calculation of the string.

Comments: This function is useful for storing code in a database text field for later calculations.

Example

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<?php $string = "beautiful"; $time = "winter"; $str = 'This is a $string $time morning!'; echo $str. "<br />";   eval("$str = "$str";"); echo $str; ?> 　　

输出：

This is a $string $time morning! This is a beautiful winter morning!  

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<br />eval() 函数在CodeIgniter框架里也有用到。在 /system/database/DB.php 文件中，根据系统的配置动态的定义了一个类 CI_DB，具体代码片段如下：

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if ( ! isset($active_record) OR $active_record == TRUE)     {         require_once(BASEPATH.'database/DB_active_rec.php');           if ( ! class_exists('CI_DB'))         {             eval('class CI_DB extends CI_DB_active_record { }');         }     }     else     {         if ( ! class_exists('CI_DB'))         {             eval('class CI_DB extends CI_DB_driver { }');         }     }       require_once(BASEPATH.'database/drivers/'.$params['dbdriver'].'/'.$params['dbdriver'].'_driver.php');       // Instantiate the DB adapter     $driver = 'CI_DB_'.$params['dbdriver'].'_driver';     $DB = new $driver($params);

　

http://www.bkjia.com/PHPjc/1135472.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/1135472.htmlTechArticlePHP eval() function, phpeval function definition and usage The eval() function calculates the string according to the PHP code. The string must be valid PHP code and must end with a semicolon. If...