PHPeval () function, phpeval function _ PHP Tutorial-php Tutorial

PHPeval () function, phpeval function. PHPeval () function, phpeval function definition and usage eval () function calculate the string according to PHP code. The string must be a valid PHP code and must end with a semicolon. If PHP eval () function, phpeval function
Definition and usage

The eval () function calculates the string according to the PHP code.

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

If the return statement is not called in the code string, NULL is returned. If a parsing error exists in the code, the eval () function returns false.

Syntax?

eval(phpcode)

　　

Parameters	Description
Phpcode	Required. Specifies the PHP code to be calculated.

Tips and comments

Note: The Return statement immediately terminates string calculation.

Note: This function is useful for storing code in database text fields for future computation.

Example?

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

Output:

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

The eval () function is also useful in the CodeIgniter framework. In the/system/database/DB. php file, a class CI_DB is dynamically defined according to the system configuration. the specific code snippet is as follows:

?

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);

　　

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