Return PHP error constant (such as E_USER_ERROR) from function, or use trigger_error?

Question

Which would you recommend?

Return an error code, such as E_USER_ERROR from a function, and determine proper message higher up:

function currentScriptFilename()
{
  if(!isset($_SERVER['SCRIPT_FILENAME']))
  {
    //This?
    return E_USER_ERROR;
  }
  else
  {
    $url = $_SERVER['SCRIPT_FILENAME'];
    $exploded = explode('/', $url);
    return end($exploded);
  }
}

Execute trigger_error() from the function, with a specific error message:

function currentScriptFilename()
{
  if(!isset($_SERVER['SCRIPT_FILENAME']))
  {
    //Or this?
    trigger_error('$_SERVER[\'SCRIPT_FILENAME\'] is not set.', E_USER_ERROR);
  }
  else
  {
    $url = $_SERVER['SCRIPT_FILENAME'];
    $exploded = explode('/', $url);
    return end($exploded);
  }
}

I am not sure if I will regret having put a bunch of error messages in my functions further down the line, since I would like to use them for other projects.

Or, would you recommend something totally different?

Your Common Sense · Accepted Answer · 2010-06-05 02:31:52Z

1

Do not mix the matters.
Error notification and error handling are different tasks.

You have to use both methods simultaneously.
If you think that $_SERVER['SCRIPT_FILENAME'] availability is worth an error message, you can use trigger error. However PHP itself will throw a notice if you won't check it.

If you want to handle this error, just check this function's return value.
But I would not create a special function for this task.

So,

if (!$filename = basename($_SERVER['SCRIPT_FILENAME']) {
  //  do whatever you want to handle this error.
}

would be enough

Exceptions could be useful to handle errors, to know if we had any errors occurred.

A simple example:

try {
  $filename = basename($_SERVER['SCRIPT_FILENAME']) 
  if (!$filename) throw new Exception("no filename");

  $data = get_some_data_from_db() or throw new Exception("no data");

  $template = new Template();
 //Exception could be thrown inside of Template class as well.
}
catch (Exception $e) {
  //if we had any errors
  show_error_page();
}
$template->show();

edited Jun 5, 2010 at 2:31

answered Jun 5, 2010 at 2:06

Your Common Sense

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2 Comments

Mike Moore Over a year ago

Thanks for pointing out basename! Your example of throwing exceptions is very helpful. I have been spending the last week reading articles and trying out handling errors and exceptions in my projects.

Christian Over a year ago

Adding to your comment; you usually trigger/raise/throw errors, not return them. However, you may return success states (true/false, file/null, resource/null, object/null ...).

Ignacio Vazquez-Abrams · Accepted Answer · 2010-06-05 01:58:22Z

1

3.Use exceptions.

answered Jun 5, 2010 at 1:58

Ignacio Vazquez-Abrams

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4 Comments

Mike Moore Over a year ago

Would you mind explaining why you would use exceptions in this case?

Ignacio Vazquez-Abrams Over a year ago

They provide an unambiguous indication that you've hit an exceptional situation. They can't be implicitly ignored, only handled somehow.

Your Common Sense Over a year ago

well the question remains the same - where to throw an exception - inside or outside :)

Andrew Moore Over a year ago

@Col. Shrapnel: Inside the function.

Wrikken · Accepted Answer · 2010-06-05 01:59:54Z

1

If this is the route you are going, I'd rather recommend throwing Exceptions rather then returing an E_ERROR (E_USER_ERROR should be used), as this is just an integer, and possibly a totally valid return for your function.

Advantages:
- Throwing of an Exception cannot be interpreted as anything else then an error by mistake.
- You keep the possibility to add a descriptive error message, even though you don't handle the error at that point/
- You keep a backtrace in your Exception.
- You can catch specific exceptions at specific points, making the decision where in your project a specific type of error should be handled a lot easier.

answered Jun 5, 2010 at 1:59

Wrikken

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Comments

alex · Accepted Answer · 2010-06-05 02:00:41Z

0

If not using exceptions which you should be, use trigger_error().

If it is an error you'd like to deal with, try returning FALSE like a lot of the in built functions do.

If you do use exceptions, catch them like this

try {
    whatever()
} catch (Exception $e) {
    // handle however
}

answered Jun 5, 2010 at 2:00

alex

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3 Comments

Mike Moore Over a year ago

Are you saying that I should use exceptions in this specific example? Or across the board?

alex Over a year ago

Well if you are using PHP5 then I would go with exceptions.

Your Common Sense Over a year ago

@letseatfood across the board but not in this simple case. Exceptions mostly used to handle errors, to control the program flow, rather than for the the error notification.

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