<chapter id="features.error-handling">
<title>Error Handling</title>
<para>
There are several types of errors and warnings in PHP. They are:
<table>
<title>PHP error types</title>
<tgroup cols="4">
<thead>
<row>
<entry>Value</entry>
<entry>Constant</entry>
<entry>Description</entry>
<entry>Note</entry>
</row>
</thead>
<tbody>
<row>
<entry>1</entry>
<entry>E_ERROR</entry>
<entry>fatal run-time errors</entry>
<entry></entry>
</row>
<row>
<entry>2</entry>
<entry>E_WARNING</entry>
<entry>run-time warnings (non fatal errors)</entry>
<entry></entry>
</row>
<row>
<entry>4</entry>
<entry>E_PARSE</entry>
<entry>compile-time parse errors</entry>
<entry></entry>
</row>
<row>
<entry>8</entry>
<entry>E_NOTICE </entry>
<entry>
run-time notices (less serious than warnings)
</entry>
<entry></entry>
</row>
<row>
<entry>16</entry>
<entry>E_CORE_ERROR</entry>
<entry>fatal errors that occur during PHP's initial startup</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>32</entry>
<entry>E_CORE_WARNING</entry>
<entry>
warnings (non fatal errors) that occur during PHP's initial
startup
</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>64</entry>
<entry>E_COMPILE_ERROR</entry>
<entry>fatal compile-time errors</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>128</entry>
<entry>E_COMPILE_WARNING</entry>
<entry>compile-time warnings (non fatal errors)</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>256</entry>
<entry>E_USER_ERROR</entry>
<entry>user-generated error message</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>512</entry>
<entry>E_USER_WARNING</entry>
<entry>user-generated warning message</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry>1024</entry>
<entry>E_USER_NOTICE </entry>
<entry>user-generated notice message</entry>
<entry>PHP 4 only</entry>
</row>
<row>
<entry></entry>
<entry>E_ALL</entry>
<entry>all of the above, as supported</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
The above values (either numerical or symbolic) are used to build
up a bitmask that specifies which errors to report. You can use the
<link linkend="language.operators.bitwise">bitwise operators</link>
to combine these values or mask out certain types of errors. Note
that only '|', '~', '!', and '&' will be understood within
<filename>php.ini</filename>, however, and that no bitwise
operators will be understood within <filename>php3.ini</filename>.
</para>
<para>
In PHP 4, the default <link
linkend="ini.error-reporting">error_reporting</link> setting is
<literal>E_ALL & ~E_NOTICE</literal>, meaning to display all errors
and warnings which are not E_NOTICE-level. In PHP 3, the default
setting is <literal>(E_ERROR | E_WARNING | E_PARSE)</literal>,
meaning the same thing. Note, however, that since constants are not
supported in PHP 3's <filename>php3.ini</filename>, the <link
linkend="ini.error-reporting">error_reporting</link> setting there
must be numeric; hence, it is <literal>7</literal>.
</para>
<para>
The initial setting can be changed in the ini file with the <link
linkend="ini.error-reporting">error_reporting</link> directive, in
your Apache <filename>httpd.conf</filename> file with the
php_error_reporting (php3_error_reporting for PHP 3) directive, and
lastly it may be set at runtime within a script by using the
<function>error_reporting</function> function.
</para>
<warning>
<para>
When upgrading code or servers from PHP 3 to PHP 4 you should
check these settings and calls to
<function>error_reporting</function> or you might disable
reporting the new error types, especially E_COMPILE_ERROR. This
may lead to empty documents without any feedback of what happened
or where to look for the problem.
</para>
</warning>
<para>
All <link linkend="language.expressions">PHP expressions</link> can
also be called with the "@" prefix, which turns off error reporting
for that particular expression. If an error occurred during such
an expression and the <link
linkend="ini.track-errors">track_errors</link> feature is enabled,
you can find the error message in the global variable
<literal>$php_errormsg</literal>.
</para>
<note>
<para>
The <link linkend="language.operators.errorcontrol">@
error-control operator</link> prefix will not disable messages
that are the result of parse errors.
</para>
</note>
<warning>
<para>
Currently the <link linkend="language.operators.errorcontrol">@
error-control operator</link> prefix will even disable error
reporting for critical errors that will terminate script
execution. Among other things, this means that if you use <link
linkend="language.operators.errorcontrol">@</link> to suppress
errors from a certain function and either it isn't available or
has been mistyped, the script will die right there with no
indication as to why.
</para>
</warning>
<para>
Below we can see an example of using the error handling capabilities in
PHP. We define a error handling function which logs the information into
a file (using an XML format), and e-mails the developer in case a critical
error in the logic happens.
<example>
<title>Using error handling in a script</title>
<programlisting role="php">
<?php
// we will do our own error handling
error_reporting(0);
// user defined error handling function
function userErrorHandler ($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 2,8,256,512 and 1024
$errortype = array (
1 => "Error",
2 => "Warning",
4 => "Parsing Error",
8 => "Notice",
16 => "Core Error",
32 => "Core Warning",
64 => "Compile Error",
128 => "Compile Warning",
256 => "User Error",
512 => "User Warning",
1024=> "User Notice"
);
// 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."</errnumber>\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 ($errno == E_USER_ERROR)
mail("phpdev@mydomain.com","Critical User Error",$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";
?>
</programlisting>
</example>
This is just a simple example showing how to use the
<link linkend="ref.errorfunc">Error Handling and Logging
functions</link>.
</para>
<para>
See also <function>error_reporting</function>,
<function>error_log</function>,
<function>set_error_handler</function>,
<function>restore_error_handler</function>,
<function>trigger_error</function>,
<function>user_error</function>
</para>
</chapter>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
-->