“Wrong parameters for Exception” when creating Exception subclass

问题

This is my code

class MyException extends Exception
{
   public function __construct($message, $code=0, Exception $previous = null) {
   parent::__construct($message,$code,$previous);
  }
   public function __toString() {
   return __CLASS__. ":[{$this->code}]:{$this->message}\n";
  }
}

Here is the error

Fatal error: Wrong parameters for Exception([string $exception [, long $code ]]) on line 5

means on this line

parent::__construct($message,$code,$previous);

What is going wrong?

回答1:

As noted in the comments, and on the Exception constructor page, the $previous argument was added in PHP 5.3.

This is reflected in the error message:

Wrong parameters for Exception ([string $exception [, long $code ]])

PHP is being a bit zealous in making sure that the constructor matches exactly. Exceptions are an important part of the internal bits, and getting them exactly right is worth being pedantic.

This code demo shows the various ways older PHP versions treat the incorrect parameter count. From the wording used above, you're using PHP 5.1 or 5.2.

Please be aware that at time of writing this (February 2014), versions of PHP prior to 5.4 have reached end of life for security and bug fix updates, and 5.4 is scheduled for EOL in summer 2014.

If you can, please make sure that you're using a modern version of PHP when deploying your application.

来源：https://stackoverflow.com/questions/21684388/wrong-parameters-for-exception-when-creating-exception-subclass