How can I get PHP to produce a backtrace upon erro

Question

Trying to debug PHP using its default current-line-only error messages is horrible. How can I get PHP to produce a backtrace (stack trace) when errors are produced?

Answer 1

As php debug extensions, there is Xdebug and PHP DBG. Each one has its advantages and disadvantages.

Answer 2

This is how you do it:

set_error_handler(function($errorType){
    if(error_reporting() & $errorType){
        ?><pre><?
        debug_print_backtrace();
        ?></pre><?
    }
}) ;

It requires PHP 5.3+ since it uses a closure. If you need lower PHP support just convert the closure to a normal function.

Answer 3

My script for installing an error handler that produces a backtrace:

<?php
function process_error_backtrace($errno, $errstr, $errfile, $errline, $errcontext) {
    if(!(error_reporting() & $errno))
        return;
    switch($errno) {
    case E_WARNING      :
    case E_USER_WARNING :
    case E_STRICT       :
    case E_NOTICE       :
    case E_USER_NOTICE  :
        $type = 'warning';
        $fatal = false;
        break;
    default             :
        $type = 'fatal error';
        $fatal = true;
        break;
    }
    $trace = array_reverse(debug_backtrace());
    array_pop($trace);
    if(php_sapi_name() == 'cli') {
        echo 'Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ':' . "\n";
        foreach($trace as $item)
            echo '  ' . (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()' . "\n";
    } else {
        echo '<p class="error_backtrace">' . "\n";
        echo '  Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ':' . "\n";
        echo '  <ol>' . "\n";
        foreach($trace as $item)
            echo '    <li>' . (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()</li>' . "\n";
        echo '  </ol>' . "\n";
        echo '</p>' . "\n";
    }
    if(ini_get('log_errors')) {
        $items = array();
        foreach($trace as $item)
            $items[] = (isset($item['file']) ? $item['file'] : '<unknown file>') . ' ' . (isset($item['line']) ? $item['line'] : '<unknown line>') . ' calling ' . $item['function'] . '()';
        $message = 'Backtrace from ' . $type . ' \'' . $errstr . '\' at ' . $errfile . ' ' . $errline . ': ' . join(' | ', $items);
        error_log($message);
    }
    if($fatal)
        exit(1);
}

set_error_handler('process_error_backtrace');
?>

Caveat: it is powerless to affect various 'PHP Fatal Errors', since Zend in their wisdom decided that these would ignore set_error_handler(). So you still get useless final-location-only errors with those.

Answer 4

Xdebug prints a backtrace table on errors, and you don't have to write any PHP code to implement it.

Downside is you have to install it as a PHP extension.

Answer 5

$backtrace = debug_backtrace();

i wrote a little article about backtracing a while back

Answer 6

PHP DeBugger also does a back trace similiar to PHP Error with more options.
If you want you can easily make your own with set_error_handler and debug_backtrace

set_error_handler ($error_handler, error_reporting);
/**
 * @var int $errno the error number
 * @var string $errstr the error message
 * @var string $errfile the error file
 * @var int $errline the line of the error
 */
$error_handler = function($errno, $errstr, $errfile, $errline){
    $trace = debug_backtrace();
    array_shift($backtrace);//remove the stack about this handler
    foreach($trace as $k => $v){
        //parse your backtrace
    }
}

Also note that for internal stacks in the backtrace some of the keys will not be set. Be sure to check if the key exist before you do something with it if you have all errors on :)