PHP
Error Handling
The default
error handling in PHP is very simple. An error message with filename, line
number and a message describing the error is sent to the browser.
PHP
Error Handling
When
creating scripts and web applications, error handling is an important part. If
your code lacks error checking code, your program may look very unprofessional
and you may be open to security risks.
This
tutorial contains some of the most common error checking methods in PHP.
We will show
different error handling methods:
Simple
"die()" statements
Custom
errors and error triggers
Error
reporting
Basic Error
Handling: Using the die() function
The first
example shows a simple script that opens a text file:
<?php
$file=fopen("welcome.txt","r");
?>
If the file
does not exist you might get an error like this:
Warning:
fopen(welcome.txt) [function.fopen]: failed to open stream:
No such file
or directory in C:\webfolder\test.php on line 2
To prevent
the user from getting an error message like the one above, we test whether the
file exist before we try to access it:
<?php
if(!file_exists("welcome.txt"))
{
die("File not found");
}
else {
$file=fopen("welcome.txt","r");
}
?>
Now if the
file does not exist you get an error like this:
File not
found
The code
above is more efficient than the earlier code, because it uses a simple error
handling mechanism to stop the script after the error.
However,
simply stopping the script is not always the right way to go. Let's take a look
at alternative PHP functions for handling errors.
Creating a
Custom Error Handler
Creating a
custom error handler is quite simple. We simply create a special function that
can be called when an error occurs in PHP.
This
function must be able to handle a minimum of two parameters (error level and
error message) but can accept up to five parameters (optionally: file,
line-number, and the error context):
Syntax
error_function(error_level,error_message,
error_file,error_line,error_context)
Parameter Description
error_level Required. Specifies the error report level
for the user-defined error. Must be a value number. See table below for
possible error report levels
error_message Required. Specifies the error message for the
user-defined error
error_file Optional. Specifies the filename in which the
error occurred
error_line Optional. Specifies the line number in
which the error occurred
error_context Optional. Specifies an array containing
every variable, and their values, in use when the error occurred
Error Report
levels
These error
report levels are the different types of error the user-defined error handler
can be used for:
Value Constant Description
2 E_WARNING Non-fatal
run-time errors. Execution of the script is not halted
8 E_NOTICE Run-time
notices. The script found something that might be an error, but could also
happen when running a script normally
256 E_USER_ERROR Fatal user-generated error. This is like an E_ERROR set by the
programmer using the PHP function trigger_error()
512 E_USER_WARNING Non-fatal user-generated warning. This is like an E_WARNING set
by the programmer using the PHP function trigger_error()
1024 E_USER_NOTICE User-generated
notice. This is like an E_NOTICE set by the programmer using the PHP function
trigger_error()
4096 E_RECOVERABLE_ERROR Catchable fatal error. This is like an E_ERROR but can be caught by
a user defined handle (see also set_error_handler())
8191 E_ALL All
errors and warnings (E_STRICT became a part of E_ALL in PHP 5.4)
Now lets
create a function to handle errors:
function
customError($errno, $errstr) {
echo "<b>Error:</b> [$errno]
$errstr<br>";
echo "Ending Script";
die();
}
The code
above is a simple error handling function. When it is triggered, it gets the
error level and an error message. It then outputs the error level and message
and terminates the script.
Now that we
have created an error handling function we need to decide when it should be
triggered.
Set Error
Handler
The default
error handler for PHP is the built in error handler. We are going to make the
function above the default error handler for the duration of the script.
It is
possible to change the error handler to apply for only some errors, that way
the script can handle different errors in different ways. However, in this
example we are going to use our custom error handler for all errors:
set_error_handler("customError");
Since we
want our custom function to handle all errors, the set_error_handler() only
needed one parameter, a second parameter could be added to specify an error
level.
Example
Testing the
error handler by trying to output variable that does not exist:
<?php
//error
handler function
function
customError($errno, $errstr) {
echo "<b>Error:</b> [$errno]
$errstr";
}
//set
error handler
set_error_handler("customError");
//trigger
error
echo($test);
?>
The output
of the code above should be something like this:
Error: [8]
Undefined variable: test
Trigger an
Error
In a script
where users can input data it is useful to trigger errors when an illegal input
occurs. In PHP, this is done by the trigger_error() function.
Example
In this
example an error occurs if the "test" variable is bigger than
"1":
<?php
$test=2;
if
($test>=1) {
trigger_error("Value must be 1 or
below");
}
?>
The output
of the code above should be something like this:
Notice:
Value must be 1 or below
in
C:\webfolder\test.php on line 6
An error can
be triggered anywhere you wish in a script, and by adding a second parameter,
you can specify what error level is triggered.
Possible
error types:
E_USER_ERROR
- Fatal user-generated run-time error. Errors that can not be recovered from.
Execution of the script is halted
E_USER_WARNING
- Non-fatal user-generated run-time warning. Execution of the script is not
halted
E_USER_NOTICE
- Default. User-generated run-time notice. The script found something that
might be an error, but could also happen when running a script normally
Example
In this
example an E_USER_WARNING occurs if the "test" variable is bigger
than "1". If an E_USER_WARNING occurs we will use our custom error
handler and end the script:
<?php
//error
handler function
function
customError($errno, $errstr) {
echo "<b>Error:</b> [$errno]
$errstr<br>";
echo "Ending Script";
die();
}
//set
error handler
set_error_handler("customError",E_USER_WARNING);
//trigger
error
$test=2;
if
($test>=1) {
trigger_error("Value must be 1 or
below",E_USER_WARNING);
}
?>
The output
of the code above should be something like this:
Error: [512]
Value must be 1 or below
Ending
Script
Now that we
have learned to create our own errors and how to trigger them, lets take a look
at error logging.
Error
Logging
By default,
PHP sends an error log to the server's logging system or a file, depending on
how the error_log configuration is set in the php.ini file. By using the
error_log() function you can send error logs to a specified file or a remote
destination.
Sending
error messages to yourself by e-mail can be a good way of getting notified of
specific errors.
Send an
Error Message by E-Mail
In the
example below we will send an e-mail with an error message and end the script,
if a specific error occurs:
<?php
//error
handler function
function
customError($errno, $errstr) {
echo "<b>Error:</b> [$errno]
$errstr<br>";
echo "Webmaster has been notified";
error_log("Error: [$errno]
$errstr",1,
"someone@example.com","From:
webmaster@example.com");
}
//set
error handler
set_error_handler("customError",E_USER_WARNING);
//trigger
error
$test=2;
if
($test>=1) {
trigger_error("Value must be 1 or
below",E_USER_WARNING);
}
?>
The output
of the code above should be something like this:
Error: [512]
Value must be 1 or below
Webmaster
has been notified
And the mail
received from the code above looks like this:
Error: [512]
Value must be 1 or below
This should
not be used with all errors. Regular errors should be logged on the server
using the default PHP logging system.
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