trigger_error

the idea is never to give out file names, line numbers, and cryptic codes to the user. Use trigger_error() after you used set_error_handler() to register your own callback function which either logs or emails the error codes to you, and echo a simple friendly message to the user.

And turn on a more verbose error handler function when you need to debug your scripts. In my init.php scripts I always have:

if (_DEBUG_) {
    set_error_handler ('debug_error_handler');
}
else {
    set_error_handler ('nice_error_handler');
}

Beware, trigger_error() is absolutely useless for transporting your own function's error messages in $php_errormsg:ini_set('track_errors', TRUE);function x() { trigger_error('MY ERROR'); }@x();echo "Error 1: \\"$php_errormsg\\"\\n";@file_get_contents('/nonexisting');echo "Error 2: \\"$php_errormsg\\"\\n";This outputs:Error 1: ""Error 2: "failed to open stream: No such file or directory"This behaviour is consistent with the description of $php_errormsg, which says that the variable will only be available within the scope in which the error occurred. The problem can be worked around with a custom error handler like the one below. However, I'm undecided whether changing the language in this way is good:function errHandler($errno, $errstr, $errfile, $errline) {  global $php_errormsg; $php_errormsg = $errstr;}set_error_handler('errHandler');

trigger_error always reports the line and file that trigger_error was called on. Which isn't very useful.

eg:

main.php:
<?php
include('functions.php');
$x = 'test';
doFunction($x);
?>

functions.php:
<?php
function doFunction($var) {
if(is_numeric($var)) {
 /* do some stuff*/
} else {
 trigger_error('var must be numeric');
}
}
?>

will output "Notice: var must be numeric in functions.php on line 6"
whereas "Notice: var must be numeric in main.php on line 4" would be more useful

here's a function to do that:

<?php

function error($message, $level=E_USER_NOTICE) {
$caller = next(debug_backtrace());
trigger_error($message.' in <strong>'.$caller['function'].'</strong> called from <strong>'.$caller['file'].'</strong> on line <strong>'.$caller['line'].'</strong>'."\n<br />error handler", $level);
}
?>

So now in our example:

main.php:
<?php
include('functions.php');
$x = 'test';
doFunction($x);
?>

functions.php:
<?php
function doFunction($var) {
    if(is_numeric($var)) {
         /* do some stuff*/
    } else {
         error('var must be numeric');
    }
}

function error($message, $level=E_USER_NOTICE) {
    $caller = next(debug_backtrace());
    trigger_error($message.' in <strong>'.$caller['function'].'</strong> called from <strong>'.$caller['file'].'</strong> on line <strong>'.$caller['line'].'</strong>'."\n<br />error handler", $level);
}
?>

now outputs:

"Notice: var must be numeric in doFunction called from main.php on line 4"

For those of you looking to use your own file or line number in the error (possibly using debug_backtrace()) instead of the ones created by trigger_error(), here is a solution:Create a custom function to handle E_USER_ERRORs that simply outputs the error type and message, while excluding the line number and file trigger_error() reports. You may also configure it to handle user warnings and notices if necessary (I did in the example below).<?phpfunction error_handler($level, $message, $file, $line, $context) {    //Handle user errors, warnings, and notices ourself    if($level === E_USER_ERROR || $level === E_USER_WARNING || $level === E_USER_NOTICE) {        echo '<strong>Error:</strong> '.$message;        return(true); //And prevent the PHP error handler from continuing    }    return(false); //Otherwise, use PHP's error handler}function trigger_my_error($message, $level) {    //Get the caller of the calling function and details about it    $callee = next(debug_backtrace());    //Trigger appropriate error    trigger_error($message.' in <strong>'.$callee['file'].'</strong> on line <strong>'.$callee['line'].'</strong>', $level);}//Use our custom handlerset_error_handler('error_handler');//-------------------------------//Demo usage://-------------------------------function abc($str) {    if(!is_string($str)) {        trigger_my_error('abc() expects parameter 1 to be a string', E_USER_ERROR);    }}abc('Hello world!'); //Worksabc(18); //Error: abc() expects parameter 1 to be a string in [FILE].php on line 31?>This is a pretty simple concept and I'm sure most of you know this, but for those that don't, let it serve as a good example!

If error_type is E_USER_ERROR then trigger_error throw FATAL ERROR and script stopped after this line.<?php$msg = 'This is the test message for echo';trigger_error('Error message', E_USER_ERROR); // Script stopped after this line...echo $msg; // This line does not appear...?>

The function trigger_error will terminate the script if $error_level is equal or higher than E_USER_ERROR. If you write your own error handler you will have to do these yourself.Example in which we assume the global LOG constant points to a PSR2 logging interface.<?phpset_error_handler( function ($errno, $errstr, $errfile, $errline) {    // error was suppressed with the @-operator    if( 0 === error_reporting() ) {        return false;    }    switch($errno) {        default:            LOG->error( "Unknown error type: [$errno] $errstr", [ 'file' => $errfile, '@' => $errline ] );            exit(1);        case E_USER_ERROR: // fall through        case E_WARNING: // treat PHP warnings are errors            LOG->error( $errstr, [ 'file' => $errfile, '@' => $errline ] );            exit(1);        case E_USER_DEPRECATED:        case E_DEPRECATED:            LOG->error( "DEPRECATED $errstr", [ 'file' => $errfile, '@' => $errline ] );            break;        case E_USER_WARNING: // fall through        case E_NOTICE: // treat PHP notices are warnings            LOG->warning( $errstr, [ 'file' => $errfile, '@' => $errline ] );            break;        case E_USER_NOTICE:            LOG->notice( $errstr, [ 'file' => $errfile, '@' => $errline ] );            break;        case E_ERROR: // fall through        case E_RECOVERABLE_ERROR:            LOG->critical( $errstr, [ 'file' => $errfile, '@' => $errline ] );            exit(1);    }    /* Don't execute PHP internal error handler */    return true;} );?>