Errors and ErrorManagement
Errors are an integral part of every computer language—although one
that, most of the time, programmers would rather not have to deal with! PHP
has some excellent facilities for dealing with errors that provide an
excellent level of fine-grained control over how errors are thrown, handled
and reported.
Proper error management is essential towriting applications that are both
stable and capable of detecting when the inevitable problem arises, thus
handling failure in a graceful manner.
Types of Errors
There are several types of errors—usually referred to as error levels in PHP:
-
Parse error: A problem with the syntax of your
program, such as leaving a semicolon off of the end of a statement. The
interpreter stops running your program when it encounters a parse error.
-
Fatal error: A severe problem with the content of
your program, such as calling a function that hasn't been defined. The
interpreter stops running your program when it encounters a fatal error.
-
Warning: An advisory from the interpreter that
something is fishy in your program, but the interpreter can keep going.
Using the wrong number of arguments when you call a function causes a
warning.
-
Notice: A tip from the PHP interpreter, playing
the role of Miss Manners. For example, printing a variable without first
initializing it to some value generates a notice.
- Strict notice: An admonishment from the PHP interpreter about your coding style. Most of these have to do with esoteric features that changed between PHP 4 and PHP 5, so you're not likely to run into them too much.
Error Reporting
By default, PHP reports any errors it encounters to the script’s
output. Unless you happen to be in a debugging environment, this is rarely
a feature that you will want to take advantage of: allowing users to see
the errors that your scripts encounter is not just bad form—it could
be a significant security issue.
Luckily, several configuration directives in the php.ini
file allow you to fine-tune how—and which—errors are
reported.
The most important ones are error_reporting, display_errors and
log_errors.
The error_reporting directive determines which errors are reported by PHP.
A series of built-in constants allow you to prevent PHP from reporting
errors beneath a certain pre-defined level. For example, the following
allows for the reporting of all errors, except notices:
error_reporting=E_ALL & ~E_NOTICE
Error reporting can also be changed dynamically from within a script by calling theerror_reporting() function.
The display_errors and log_errors directives can be used to determine how errors are reported. If display_errors is turned on, errors are outputted to the script’s output; generally speaking, this is not desirable in a production environment, as everyone will be able to see your scripts’ errors. Under those circumstances, you will instead want to turn on log_errors, which causes errors to be written to your web server’s error log.
Handling Errors
Your scripts should always be able to recover from a trappable
error—even if it’s just to advise the user that an error
occurred and notify support staff of the same fact. This way, your script
won’t simply capitulate when something unexpected
occurs—resulting in better communication with your customers and the
possible avoidance of some major problems.
Luckily, error handling is very easy. Your scripts can declare a catch-all
function that is called by PHP when an error condition occurs by calling
theset_error_handler() function:
$oldErrorHandler = ’’;
function myErrorHandler ($errNo, $errStr,
$errFile, $errLine, $errContext) {
logToFile("Error $errStr in $errFile at line $errLine");
// Call the
old error handler
if
($oldErrorHandler) {
$oldErrorHandler ($errNo, $errStr, $errFile, $errLine, $errContext);
}
}
$oldErrorHandler = set_error_handler
($oldErrorHandler);
As you can see, the function name of the old error handler (if any) is
returned by the call to set_error_handler()—this
allows you to stack several error handlers on top of each other, thus
making it possible to have different functions handle different kinds of
errors.
It’s important to keep in mind that your error handlerwill
completely bypass PHP’s errormechanism—meaning that you will be
responsible for handling all errors, and stopping the script’s
execution if necessary.
|
This page was last modified on 18 Nov 2010 at 14:06:24. |
Gautam Kumar EDP Manager  http://www.w3schools.in |
 |
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