XXXIII. 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

NameDefaultChangeableChangelog
error_reportingNULLPHP_INI_ALL 
display_errors"1"PHP_INI_ALL 
display_startup_errors"0"PHP_INI_ALLAvailable since PHP 4.0.3.
log_errors"0"PHP_INI_ALL 
log_errors_max_len"1024"PHP_INI_ALLAvailable since PHP 4.3.0.
ignore_repeated_errors"0"PHP_INI_ALLAvailable since PHP 4.3.0.
ignore_repeated_source"0"PHP_INI_ALLAvailable since PHP 4.3.0.
report_memleaks"1"PHP_INI_ALLAvailable since PHP 4.3.0.
track_errors"0"PHP_INI_ALL 
html_errors"1"PHP_INI_ALLPHP_INI_SYSTEM in PHP <= 4.2.3. Available since PHP 4.0.2.
docref_root""PHP_INI_ALLAvailable since PHP 4.3.0.
docref_ext""PHP_INI_ALLAvailable since PHP 4.3.2.
error_prepend_stringNULLPHP_INI_ALL 
error_append_stringNULLPHP_INI_ALL 
error_logNULLPHP_INI_ALL 
warn_plus_overloadingNULLPHP_INI?? 
For further details and definitions of the PHP_INI_* constants, see the Appendix H.

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.

PHP Constants outside of PHP: Using PHP Constants outside of PHP, like in httpd.conf, will have no useful meaning so in such cases the integer values are required. And since error levels will be added over time, the maximum value (for E_ALL) will likely change. So in place of E_ALL consider using a larger value to cover all bit fields from now and well into the future, a numeric value like 2147483647.

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.

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

ValueConstantDescriptionNote
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 5.2.0
8191 E_ALL (integer) All errors and warnings, as supported, except of level E_STRICT in PHP < 6. 6143 in PHP 5.2.x 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.

Examples

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_ERROR  => '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";

?>

See Also

See also syslog().

Table of Contents
debug_backtrace -- Generates a backtrace
debug_print_backtrace --  Prints a backtrace
error_get_last -- Get the last occurred error
error_log -- Send an error message somewhere
error_reporting -- Sets which PHP errors are reported
restore_error_handler -- Restores the previous error handler function
restore_exception_handler --  Restores the previously defined exception handler function
set_error_handler -- Sets a user-defined error handler function
set_exception_handler --  Sets a user-defined exception handler function
trigger_error -- Generates a user-level error/warning/notice message
user_error -- Alias of trigger_error()