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Now that we have our errors showing, we’re ready to get started actually addressing those errors. Errors can be output to the screen, local disk or both. PHP can also choose which error severities it will report and which it will ignore. We'll look at how to use those errors to fix your code.
Custom Function
You can define a custom function to handle errors.
function customError($errno, $errstr) {
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "Ending Script";
die();
}
set_error_handler(“customError”);
Trigger an Error
You can trigger your own errors when something doesn't meet certain requirements. PHP comes with a built-in function for this purpose called trigger_error().
$test=2;
if ($test>1) {
trigger_error("Value must be 1 or below");
}
Errors Settings
| Constant | Description |
|---|---|
| E_ERROR (integer) | Fatal run-time errors. These indicate errors that can not be recovered from, such as a memory allocation problem. Execution of the script is halted |
| E_WARNING (integer) | Run-time warnings (non-fatal errors). Execution of the script is not halted |
| E_PARSE (integer) | Compile-time parse errors. Parse errors should only be generated by the parser |
| E_NOTICE (integer) | Run-time notices. Indicate that the script encountered something that could indicate an error, but could also happen in the normal course of running a script |
| E_CORE_ERROR (integer) | Fatal errors that occur during PHP's initial startup. This is like an E_ERROR, except it is generated by the core of PHP |
| E_CORE_WARNING (integer) | Warnings (non-fatal errors) that occur during PHP's initial startup. This is like an E_WARNING, except it is generated by the core of PHP |
| E_COMPILE_ERROR (integer) | Fatal compile-time errors. This is like an E_ERROR, except it is generated by the Zend Scripting Engine |
| E_COMPILE_WARNING (integer) | Compile-time warnings (non-fatal errors). This is like an E_WARNING, except it is generated by the Zend Scripting Engine |
| E_USER_ERROR (integer) | User-generated error message. This is like an E_ERROR, except it is generated in PHP code by using the PHP function trigger_error() |
| E_USER_WARNING (integer) | User-generated warning message. This is like an E_WARNING, except it is generated in PHP code by using the PHP function trigger_error() |
| E_USER_NOTICE (integer) | User-generated notice message. This is like an E_NOTICE, except it is generated in PHP code by using the PHP function trigger_error() |
| E_STRICT (integer) | Enable to have PHP suggest changes to your code which will ensure the best interoperability and forward compatibility of your code |
| E_RECOVERABLE_ERROR (integer) | Catchable fatal error. It indicates that a probably dangerous error occurred, but did not leave the Engine in an unstable state. If the error is not caught by a user defined handle (see also set_error_handler()), the application aborts as it was an E_ERROR |
| E_DEPRECATED (integer) | Run-time notices. Enable this to receive warnings about code that will not work in future versions |
| E_USER_DEPRECATED (integer) | User-generated warning message. This is like an E_DEPRECATED, except it is generated in PHP code by using the PHP function trigger_error() |
| E_ALL (integer) | All errors and warnings, as supported, except of level E_STRICT prior to PHP 5.4.0 |
Exception Handling
In general Errors are the Procedural approach to handling errors, while Exceptions are the Object-Oriented approach. Exceptions are represented in PHP by the class Exception. Exceptions are raised using the “throw” syntax and can be caught using a “try/catch” syntax block. Any code in which an Exception error may occur should be placed in the “try” block, which can be followed by a “catch” block to handle the error.
This is what the Exception syntax looks like:
try { // throw errors in the try-block
// if an error occurs we can throw an exception
throw new Exception('this is an error.');
}
catch(Exception $e) { // catch the throws in the catch-block
// do something with the exception object, eg. display its message
echo 'Error message: ' .$e->getMessage();
}
http://code.tutsplus.com/tutorials/php-exceptions--net-22274
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Now that we have our errors showing
we're ready to get started actually
0:00
addressing those errors.
0:04
Many languages throw an exception
0:06
whenever there is any sort
of problem with the code.
0:09
These languages are what I
would call exception heavy.
0:12
PHP is an exception light language.
0:16
In most cases PHP will
output an error instead.
0:19
Like most things in PHP, you do have
quite a bit of control over which things
0:24
cause exceptions and
other advanced options handling errors.
0:28
Check out the teacher’s notes for
more information.
0:33
Errors can be output to the screen,
local disk or both.
0:37
PHP can also choose which error severities
it will report and which it will ignore.
0:41
The most common errors are E_NOTICE,
E_WARNING, and E_ERROR.
0:48
After throwing a notice or a warning,
PHP will keep executing the script.
0:53
E_ERROR or fatal errors on the other hand
halt the script in an unrecoverable way.
0:58
It can be tempting to ignore notices or
1:04
warnings since they don't really
stop things from working.
1:09
But catching and fixing those things
from the start is much better practice.
1:13
In the long run,
it's better to do things properly.
1:18
For example,
if a feature is marked as deprecated,
1:21
you probably wanna know about
it before it's removed.
1:25
Otherwise, an upgrade
becomes much harder later on.
1:29
Let's take a look at errors4.
1:34
This file is completely
full of broken stuff.
1:36
On line 3 we can see the error
reporting function being used.
1:39
This function is how we control which
severity or errors will be reported.
1:43
And this code specifically requests
that only E_ERROR, E_WARNING and
1:49
E_PARSE are reported.
1:53
An error being reported means
it can go into a log file.
1:55
And maybe be displayed down
the screen depending on the settings.
1:58
We can see in line 5 that
the display errors are turned on.
2:03
So if we preview this script in a browser,
2:08
we'll be able to see our errors because
we have display errors turned on.
2:11
Here we see int(5), so
some code seems to be working.
2:18
And we see some errors but
they're all jammed up on the same line.
2:22
This is because it's not
outputting errors as html.
2:26
It's outputting them with just text.
2:29
So let's go back and
turn on html formatting.
2:32
Much better.
2:41
Now what's really strange is that I
know from the code that I've written
2:43
that there should be four errors because
I intentionally broke a lot of stuff.
2:46
Let's take a look at our code and
see what could be wrong.
2:50
The first thing you might notice is that 5
is being added to the variable called nope
2:54
and nowhere in this code
is nope being defined.
3:00
That should throw a notice but
we aren't seeing one.
3:03
This is because we have not
requested PHP to report notices.
3:07
And as such,
3:11
an uninitialized variable will be
treated as null without any complaints.
3:13
5 plus null is 5, kinda.
3:17
But it's not great to have this
sort of code in our application.
3:22
We don't want undefined variables
floating around without any errors.
3:25
Some developers pick and
choose specific error levels like this.
3:30
But that means that sometimes
something might be forgotten.
3:34
It also means that newly added error
severities like E_DEPRECATED and
3:38
E_USERDEPRECATED would be missed.
3:42
Picking specific error levels unless
you really know what you're doing
3:46
is dangerous.
3:50
The general advice of many is to
turn the error reporting level up
3:51
as high as you can using E_ALL.
3:55
That's really easy to change.
3:58
You just remove all these specific
levels and change it to E_ALL.
4:00
Now we can save that and
preview it in the browser.
4:09
Great.
4:14
These are the four errors I'm expecting.
4:15
You can see that there is a notice
of an undefined variable, nope.
4:17
It outputs 5 because it
will still do the math.
4:21
It will just warn you about it.
4:25
Next we see a warning, creating a default
object from an empty value on line 15.
4:27
Next, we have a non static method, foobar,
should be called statically on line 22.
4:34
And finally, a fatal error,
a call to an undefined method, foo, $nope.
4:40
Let's see if we can fix these errors.
4:46
So first, $nope equals 0.
4:51
That should fix that notice.
4:57
Then we wanna define our object.
5:00
We'll set this to the standard class.
5:06
Public function bar.
5:12
This needs to be a static
function to fix that error.
5:14
And then finally,
to get rid of the final fatal error,
5:20
we need to make another
static function called $nope.
5:23
Let's see if this has worked.
5:34
Perfect.
5:38
The impossible happened.
5:39
We got to the end of the file because we
fixed all the errors thanks to reporting.
5:41
One thing to remember
is that in production
5:47
you never want your end user to see
PHP system errors on the screen.
5:50
Displaying error messages to
your site visitors can disclose
5:56
important information about your site's
setup and cause a huge security risk.
6:00
On production, you want to have
display errors turned off.
6:05
Next, let's talk about logging.
6:09
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