Summary of the usage of eval function in PHP

$string = "Beautiful"; $time = "Winter"; $str = ' This is a $string $time morning! '; echo $str. " "; Eval ("$str =" $str ";"); Echo $str; ?> Copy Code Output: This is a $string $time morning! This is a beautiful winter morning! The eval () function is also useful in the CodeIgniter framework. In the/system/database/db.php file, a class ci_db is dynamically defined according to the configuration of the system, with specific code snippets: if (! isset ($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); Copy Code This function can substitute the value of a variable in a string, and is usually used to manipulate the data on the database. The parameter code_str is the string to be processed. Note: The string to be processed conforms to the PHP string format, with a semicolon at the end. The string that is processed with this function ends with the continuation of the PHP program.

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