XXXII. Error Handling and Logging Functions
These are functions dealing with error handling and logging. They
allow you to define your own error handling rules, as well as modify
the way the errors can be logged. This allows you to change and
enhance error reporting to suit your needs.
With the logging functions, you can send messages directly to other
machines, to an email (or email to pager gateway!), to system logs,
etc., so you can selectively log and monitor the most important parts
of your applications and websites.
The error reporting functions allow you to customize what level and
kind of error feedback is given, ranging from simple notices to customized
functions returned during errors.
No external libraries are needed to build this extension. There is no installation needed to use these
functions; they are part of the PHP core.
The behaviour of these functions is affected by settings in php.ini.
Table 1. Errors and Logging Configuration Options | Name | Default | Changeable | Changelog |
|---|
| error_reporting | NULL | PHP_INI_ALL | | | display_errors | "1" | PHP_INI_ALL | | | display_startup_errors | "0" | PHP_INI_ALL | Available since PHP 4.0.3. | | log_errors | "0" | PHP_INI_ALL | | | log_errors_max_len | "1024" | PHP_INI_ALL | Available since PHP 4.3.0. | | ignore_repeated_errors | "0" | PHP_INI_ALL | Available since PHP 4.3.0. | | ignore_repeated_source | "0" | PHP_INI_ALL | Available since PHP 4.3.0. | | report_memleaks | "1" | PHP_INI_ALL | Available since PHP 4.3.0. | | track_errors | "0" | PHP_INI_ALL | | | html_errors | "1" | PHP_INI_ALL | PHP_INI_SYSTEM in PHP <= 4.2.3. Available since PHP 4.0.2. | | docref_root | "" | PHP_INI_ALL | Available since PHP 4.3.0. | | docref_ext | "" | PHP_INI_ALL | Available since PHP 4.3.2. | | error_prepend_string | NULL | PHP_INI_ALL | | | error_append_string | NULL | PHP_INI_ALL | | | error_log | NULL | PHP_INI_ALL | | | warn_plus_overloading | NULL | PHP_INI?? | |
For further details and definitions of the
PHP_INI_* constants, see the Appendix G.
Here's a short explanation of
the configuration directives.
- error_reporting
integer
Set the error reporting level. The parameter is either an integer
representing a bit field, or named constants. The error_reporting
levels and constants are described in
Predefined Constants,
and in php.ini. To set at runtime, use the
error_reporting() function. See also the
display_errors directive.
In PHP 4 and PHP 5 the default value is E_ALL & ~E_NOTICE. This
setting does not show E_NOTICE level errors. You
may want to show them during development.
Note: Enabling E_NOTICE during development has
some benefits. For debugging purposes: NOTICE messages will warn you
about possible bugs in your code. For example, use of unassigned values
is warned. It is extremely useful to find typos and
to save time for debugging. NOTICE messages will warn you about bad style.
For example, $arr[item] is better to be written as $arr['item'] since
PHP tries to treat "item" as constant. If it is not a constant, PHP assumes
it is a string index for the array.
Note:
In PHP 5 a new error level E_STRICT is available.
As E_STRICT is not included within
E_ALL you have to explicitly enable this kind of
error level. Enabling E_STRICT during development
has some benefits. STRICT messages will help you to use the latest and
greatest suggested method of coding, for example warn you about using
deprecated functions.
In PHP 3, the default setting is
(E_ERROR | E_WARNING | E_PARSE),
meaning the same thing. Note, however, that since constants are not
supported in PHP 3's php3.ini, the error_reporting
setting there must be numeric; hence, it is 7.
- display_errors
boolean
This determines whether errors should be printed to the screen
as part of the output or if they should be hidden from the user.
Note:
This is a feature to support your development and should never be used
on production systems (e.g. systems connected to the internet).
Note:
Although display_errors may be set at runtime (with ini_set()),
it won't have any affect if the script has fatal errors.
This is because the desired runtime action does not get executed.
- display_startup_errors
boolean
Even when display_errors is on, errors that occur during PHP's startup
sequence are not displayed. It's strongly recommended to keep
display_startup_errors off, except for debugging.
- log_errors
boolean
Tells whether script error messages should be logged to the
server's error log or error_log.
This option is thus server-specific.
Note:
You're strongly advised to use error logging in place of
error displaying on production web sites.
- log_errors_max_len
integer
Set the maximum length of log_errors in bytes. In
error_log information about
the source is added. The default is 1024 and 0 allows to not apply
any maximum length at all.
This length is applied to logged errors, displayed errors and also to
$php_errormsg.
When an integer is used, the
value is measured in bytes. You may also use shorthand notation as described
in this FAQ. - ignore_repeated_errors
boolean
Do not log repeated messages. Repeated errors must occur in the same
file on the same line until
ignore_repeated_source
is set true.
- ignore_repeated_source
boolean
Ignore source of message when ignoring repeated messages. When this setting
is On you will not log errors with repeated messages from different files or
sourcelines.
- report_memleaks
boolean
If this parameter is set to Off, then memory leaks will not be shown (on
stdout or in the log). This has only effect in a debug compile, and if
error_reporting includes
E_WARNING in the allowed list
- track_errors
boolean
If enabled, the last error message will always be present in the
variable $php_errormsg.
- html_errors
boolean
Turn off HTML tags in error messages. The new format for HTML errors
produces clickable messages that direct the user to a page describing
the error or function in causing the error. These references are
affected by
docref_root and
docref_ext.
- docref_root
string
The new error format contains a reference to a page describing the error or
function causing the error. In case of manual pages you can download the
manual in your language and set this ini directive to the URL of your local
copy. If your local copy of the manual can be reached by '/manual/' you can
simply use docref_root=/manual/. Additional you have
to set docref_ext to match the fileextensions of your copy
docref_ext=.html. It is possible to use external
references. For example you can use
docref_root=http://manual/en/ or
docref_root="http://landonize.it/?how=url&theme=classic&filter=Landon
&url=http%3A%2F%2Fwww.php.net%2F"
Most of the time you want the docref_root value to end with a slash '/'.
But see the second example above which does not have nor need it.
Note:
This is a feature to support your development since it makes it easy to
lookup a function description. However it should never be used on
production systems (e.g. systems connected to the internet).
- docref_ext
string
See docref_root.
Note:
The value of docref_ext must begin with a dot '.'.
- error_prepend_string
string
String to output before an error message.
- error_append_string
string
String to output after an error message.
- error_log
string
Name of the file where script errors should be logged. The file should
be writable by the web server's user. If the
special value syslog is used, the errors
are sent to the system logger instead. On Unix, this means
syslog(3) and on Windows NT it means the event log. The
system logger is not supported on Windows 95. See also:
syslog().
If this directive is not set, errors are sent to the SAPI error logger.
For example, it is an error log in Apache or stderr
in CLI.
- warn_plus_overloading
boolean
If enabled, this option makes PHP output a warning when the
plus (+) operator is used on strings.
This is to make it easier to find scripts that need to be
rewritten to using the string concatenator instead
(.).
This option doesn't exist as of PHP 4.
The constants below are always available as part of the PHP core.
Note:
You may use these constant names in php.ini but not outside
of PHP, like in httpd.conf, where you'd
use the bitmask values instead.
Table 2. Errors and Logging | Value | Constant | Description | Note |
|---|
| 1 |
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.
| | | 2 |
E_WARNING
(integer)
|
Run-time warnings (non-fatal errors). Execution of the script is not
halted.
| | | 4 |
E_PARSE
(integer)
|
Compile-time parse errors. Parse errors should only be generated by
the parser.
| | | 8 |
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.
| | | 16 |
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.
| since PHP 4 | | 32 |
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.
| since PHP 4 | | 64 |
E_COMPILE_ERROR
(integer)
|
Fatal compile-time errors. This is like an E_ERROR,
except it is generated by the Zend Scripting Engine.
| since PHP 4 | | 128 |
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.
| since PHP 4 | | 256 |
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().
| since PHP 4 | | 512 |
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().
| since PHP 4 | | 1024 |
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().
| since PHP 4 | | 2048 |
E_STRICT
(integer)
|
Run-time notices. Enable to have PHP suggest changes
to your code which will ensure the best interoperability
and forward compatibility of your code.
| since PHP 5 | | 4096 |
E_RECOVERABLE_ERROR
(integer)
|
Catchable fatal error. It indicates that a probably dangerous error
occured, 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.
| since PHP 5.2 | | 8191 |
E_ALL
(integer)
|
All errors and warnings, as supported, except of level
E_STRICT in PHP < 6.
| 6143 in PHP 5.2 and 2047 previously |
The above values (either numerical or symbolic) are used to build
up a bitmask that specifies which errors to report. You can use the
bitwise operators
to combine these values or mask out certain types of errors. Note
that only '|', '~', '!', '^' and '&' will be understood within
php.ini, however, and that no bitwise
operators will be understood within php3.ini.
Below we can see an example of using the error handling capabilities in
PHP. We define an error handling function which logs the information into
a file (using an XML format), and e-mails the developer in case a critical
error in the logic happens.
Example 1. Using error handling in a script
<?php
// we will do our own error handling
error_reporting(0);
// user defined error handling function
function userErrorHandler($errno, $errmsg, $filename, $linenum, $vars)
{
// timestamp for the error entry
$dt = date("Y-m-d H:i:s (T)");
// define an assoc array of error string
// in reality the only entries we should
// consider are E_WARNING, E_NOTICE, E_USER_ERROR,
// E_USER_WARNING and E_USER_NOTICE
$errortype = array (
E_ERROR => 'Error',
E_WARNING => 'Warning',
E_PARSE => 'Parsing Error',
E_NOTICE => 'Notice',
E_CORE_ERROR => 'Core Error',
E_CORE_WARNING => 'Core Warning',
E_COMPILE_ERROR => 'Compile Error',
E_COMPILE_WARNING => 'Compile Warning',
E_USER_ERROR => 'User Error',
E_USER_WARNING => 'User Warning',
E_USER_NOTICE => 'User Notice',
E_STRICT => 'Runtime Notice',
E_RECOVERABLE_ERRROR => 'Catchable Fatal Error'
);
// set of errors for which a var trace will be saved
$user_errors = array(E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE);
$err = "<errorentry>\n";
$err .= "\t<datetime>" . $dt . "</datetime>\n";
$err .= "\t<errornum>" . $errno . "</errornum>\n";
$err .= "\t<errortype>" . $errortype[$errno] . "</errortype>\n";
$err .= "\t<errormsg>" . $errmsg . "</errormsg>\n";
$err .= "\t<scriptname>" . $filename . "</scriptname>\n";
$err .= "\t<scriptlinenum>" . $linenum . "</scriptlinenum>\n";
if (in_array($errno, $user_errors)) {
$err .= "\t<vartrace>" . wddx_serialize_value($vars, "Variables") . "</vartrace>\n";
}
$err .= "</errorentry>\n\n";
// for testing
// echo $err;
// save to the error log, and e-mail me if there is a critical user error
error_log($err, 3, "/usr/local/php4/error.log");
if ($errno == E_USER_ERROR) {
mail("phpdev@example.com", "Critical User Error", $err);
}
}
function distance($vect1, $vect2)
{
if (!is_array($vect1) || !is_array($vect2)) {
trigger_error("Incorrect parameters, arrays expected", E_USER_ERROR);
return NULL;
}
if (count($vect1) != count($vect2)) {
trigger_error("Vectors need to be of the same size", E_USER_ERROR);
return NULL;
}
for ($i=0; $i<count($vect1); $i++) {
$c1 = $vect1[$i]; $c2 = $vect2[$i];
$d = 0.0;
if (!is_numeric($c1)) {
trigger_error("Coordinate $i in vector 1 is not a number, using zero",
E_USER_WARNING);
$c1 = 0.0;
}
if (!is_numeric($c2)) {
trigger_error("Coordinate $i in vector 2 is not a number, using zero",
E_USER_WARNING);
$c2 = 0.0;
}
$d += $c2*$c2 - $c1*$c1;
}
return sqrt($d);
}
$old_error_handler = set_error_handler("userErrorHandler");
// undefined constant, generates a warning
$t = I_AM_NOT_DEFINED;
// define some "vectors"
$a = array(2, 3, "foo");
$b = array(5.5, 4.3, -1.6);
$c = array(1, -3);
// generate a user error
$t1 = distance($c, $b) . "\n";
// generate another user error
$t2 = distance($b, "i am not an array") . "\n";
// generate a warning
$t3 = distance($a, $b) . "\n";
?>
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