


A brief discussion on the definition and usage of PHP eval() function_php example
Jul 06, 2016 pm 01:32 PMeval() 函數(shù)把字符串按照 PHP 代碼來計算。
該字符串必須是合法的 PHP 代碼,且必須以分號結(jié)尾。
如果沒有在代碼字符串中調(diào)用 return 語句,則返回 NULL。如果代碼中存在解析錯誤,則 eval() 函數(shù)返回 false。
語法
eval(phpcode)
參數(shù) | 描述 |
---|---|
phpcode | 必需。規(guī)定要計算的 PHP 代碼。 |
提示和注釋
注釋:返回語句會立即終止對字符串的計算。
注釋:該函數(shù)對于在數(shù)據(jù)庫文本字段中供日后計算而進行的代碼存儲很有用。
例子
<?php $string = "beautiful"; $time = "winter"; $str = 'This is a $string $time morning!'; echo $str. "<br />"; eval("\$str = \"$str\";"); echo $str; ?>
輸出:
This is a $string $time morning!
This is a beautiful winter morning!
eval() 函數(shù)在CodeIgniter框架里也有用到。在 /system/database/DB.php 文件中,根據(jù)系統(tǒng)的配置動態(tài)的定義了一個類 CI_DB,具體代碼片段如下:
if ( ! isset($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);
以上這篇淺談PHP eval()函數(shù)定義和用法就是小編分享給大家的全部內(nèi)容了,希望能給大家一個參考,也希望大家多多支持腳本之家。

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