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# XXVII. Error Handling and Logging Functions

# Introduction

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.

# Requirements

No external libraries are needed to build this extension.

# Installation

There is no installation needed to use these functions; they are part of the PHP core.

# Runtime Configuration

The behaviour of these functions is affected by settings in `php.ini`.

Table 1. Errors and Logging Configuration Options

Name | Default | Changeable
--- | --- | ---
error_reporting | E_ALL & ~E_NOTICE | PHP_INI_ALL
display_errors | "1" | PHP_INI_ALL
display_startup_errors | "0" | PHP_INI_ALL
log_errors | "0" | PHP_INI_ALL
log_errors_max_len | "1024" | PHP_INI_ALL
ignore_repeated_errors | "0" | PHP_INI_ALL
ignore_repeated_source | "0" | PHP_INI_ALL
report_memleaks | "1" | PHP_INI_SYSTEM
track_errors | "0" | PHP_INI_ALL
html_errors | "1" | PHP_INI_ALL
docref_root | "http://www.php.net/" | PHP_INI_ALL
docref_ext | ".html" | PHP_INI_ALL
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 definition of the PHP_INI_* constants see ini_set().

Here is 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 the default value 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 possibls bugs in your code. For example, use of unassigned values are 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.

  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 HTML output or not.

`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 kbytes. In error_log information about the source is added. The default is 1024 and 0 allows to not apply any maximum length at all.

`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 in 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.

`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. 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().

`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 (`.`).

# Predefined Constants

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. | PHP 4 only
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. | PHP 4 only
64 | `E_COMPILE_ERROR` (integer) | Fatal compile-time errors. This is like an `E_ERROR`, except it is generated by the Zend Scripting Engine. | PHP 4 only
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. | PHP 4 only
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(). | PHP 4 only
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(). | PHP 4 only
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(). | PHP 4 only
2047 | `E_ALL` (integer) | All errors and warnings, as supported. |

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`.

# Examples

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 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 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."</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";

    ?>

# See Also

See also syslog().

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