Error handling in classes and external details

[coo_t2]

Hey all. I'm building some classes and was kinda of wondering about how
I should design the classes to handle errors if I want the classes to be
reusable.

When possible should I leave it up to the person using the object to do the
error handling. Assuming that I give them the information required to determine
that an error has taken place?


When the object needs to keep track of errors should I instantiate an object
from an error handling class to deal with the errors?


Another issue is how to get details about the enviroment/application
into a class and keep the class reusable.

For example if I had an error class that print errors, I would need
to know whether to use "\n" or "<br>" for line breaks, because I might
wanna make the script usable from the command line.
Maybe there's some other configuration variables that I will need in my classes also.
How do I use them and keep the classes that are using them reusable?

The error class would have to instantiate an "config" object or something
to get the app/enviroment details wouldn't it?


Maybe you all know of some simple examples I could look at that deal with
theses issues? I'd like to see how these problems were solved.

--ed

[KillAllDash9]

I would recommend using the "trigger_error" function. That way, if someone wants to use your class in another application, they can either take the time to write their own error handling functions, or let PHP's internal error handling display/log the errors depending on their needs. It also keeps your classes from being tied to your own error-handling classes.

[fukas78]

I recommend to you look inside the PEAR project.
There is great example how to handle errors via classes.
http://pear.php.net

[coo_t2]

I recommend to you look inside the PEAR project.
There is great example how to handle errors via classes.
http://pear.php.net

It looks like methods in the pear library return a "PEAR_Error" object.

If I understand the code correctly it doesn't look like you can
check the boolean return value of a method as usual because it
might return an object?

That means you can't do something like the following
because it might return an object:

if ($obj->doSomething() )
{   echo 'I love doing something!<br>';
} 

Is this a good thing? I like knowing that my functions will either return
true or false or something else, but not both. Am I right in thinking this?


I was thinking that maybe I could make an "error" member object in each class
that needs it.

Then maybe you could do something like this:

if ($obj->doSomething() )
{   echo 'I love doing something!<br>';
}
else
{   $errorObj = $obj->getErrorObj();
} 

Does that look reasonable?

Of course I'm also gonna have to get used to the whole try/catch way of doing
things too I guess.. ERghh..

--ed

[HarryF]

Think you use PEAR::isError() from the outside to check whether what you got back is what you expected - makes an interim solution to PHP5 and try/catch blocks.

[coo_t2]

Think you use PEAR::isError() from the outside to check whether what you got back is what you expected - makes an interim solution to PHP5 and try/catch blocks.

With try/catch I'd do something like the following wouldn't I? :

try {
    if (!$obj->doSomething() )
    {   throw new ExceptionClass('wrong buster');
    }
}
catch (ExceptionClass $exception) {
    
    $exception->toString();
} 

I read this page of that nice article and it shows how to do it from inside
and outside of the class.

Generally speaking should this type of stuff be left outside of the class
or should it be handled internally?

Will PHP5 have any predefined exception types? From the little bit I've
played around with python I know it does. I'm sure Java does too.

If not there's gonna be a gzillion exception classes all over the web written for the most common
errors by people who have no experience handling errors this way(like me ).

I think they should at least the most common ones predefined like I/O error etc..

--ed

[mukesh]

this is a small piece of code which track the error and write the description in alog file...

<html>

<head>
<title></title>
</head>

<body>

<?php
/*
Defining the function which will be called when any error occured
*/
function display_error($error,$error_string,$filename,$line,$symbols){
//fopen("the location of log file",mode)
$file= fopen("./en/emptylog/access.log",'a+');
$dat=date('r');
$msg="\n$dat ::: $error_string $filename $line \n";
//Created message to write in log file about the details fo the error
fwrite($file,$msg);
}

set_error_handler('display_error');

//where ever you want to use this functionality..just include this file and set
//set_erro_handler('functionname');
?>

</body>

</html>

[KillAllDash9]

The problem with relying on PEAR's error handling is that your scripts would be useless to anyone who doesn't have PEAR installed without a lot of modification (which is what you were trying to avoid in the first place, right?)

Everyone who uses PHP has the PHP error functions available to them, so you won't run into any problems that way.

[HarryF]

Just to post it: PEAR Error handling in detail