Here's a function I just wrote for getting a nice and comprehensible call trace. It is probably more resource-intensive than some other alternatives but it is short, understandable, and gives nice output (Exception->getTraceAsString()).

<?php
function generateCallTrace()
{
    $e = new Exception();
    $trace = explode("\n", $e->getTraceAsString());
    // reverse array to make steps line up chronologically
    $trace = array_reverse($trace);
    array_shift($trace); // remove {main}
    array_pop($trace); // remove call to this method
    $length = count($trace);
    $result = array();
    
    for ($i = 0; $i < $length; $i++)
    {
        $result[] = ($i + 1)  . ')' . substr($trace[$i], strpos($trace[$i], ' ')); // replace '#someNum' with '$i)', set the right ordering
    }
    
    return "\t" . implode("\n\t", $result);
}
?>

Example output:
    1) /var/www/test/test.php(15): SomeClass->__construct()
    2) /var/www/test/SomeClass.class.php(36): SomeClass->callSomething()

When use register_shutdown_function, and the function called when shutting down, there are no line number nor filename information about this function, only function, class(if possible), type(if possible) and args are provided.

Just a short note on debug_backtrace options for PHP 5.3.6 or newer:

debug_backtrace() - show all options
debug_backtrace(0) - exlude ["object"]
debug_backtrace(1) - same as debug_backtrace()
debug_backtrace(2) - exlude ["object"] AND ["args"]

use this example and try calling debug_backtrace with different options

<?php
function F1()
{
    echo "<br />";
    echo "in F1 now";
    echo "<pre>".print_r(debug_backtrace(2),true)."</pre>";
}

class DebugOptionsTest
{
    function F2()
    {
        echo "<br />";
        echo "in F2 now";
        F1();
    }

}

echo "<hr />calling F1";
F1();

$c=new DebugOptionsTest();
echo "<hr /><hr /><hr />calling F2";
$c->F2("testValue");

?>

If you are using the backtrace function in an error handler, avoid using var_export() on the args, as you will cause fatal errors in some situations, preventing you from seeing your stack trace.  Some structures will cause PHP to generate the fatal error "Nesting level too deep - recursive dependency?" This is a design feature of php, not a bug (see http://bugs.php.net/bug.php?id=30471)

Quick and dirty formatted output from debug_backtrace.

$file_paths = debug_backtrace();
  
foreach($file_paths AS $file_path) {
  foreach($file_path AS $key => $var) {
    if($key == 'args') {
      foreach($var AS $key_arg => $var_arg) {
        echo $key_arg . ': ' . $var_arg . '<br>';
      }
    } else {
      echo $key . ': ' . $var . '<br>';
    }  
  }
}

Be carefull if you are using objects as arguments for function calls!

<?php
error_reporting(E_ALL);

function myPrint($trace){
    foreach($trace as $i=>$call){
        /**
         * THIS IS NEEDED! If all your objects have a __toString function it's not needed!
         * 
         * Catchable fatal error: Object of class B could not be converted to string
         * Catchable fatal error: Object of class A could not be converted to string
         * Catchable fatal error: Object of class B could not be converted to string
         */
        if (is_object($call['object'])) { $call['object'] = 'CONVERTED OBJECT OF CLASS '.get_class($call['object']); }
        if (is_array($call['args'])) {
            foreach ($call['args'] AS &$arg) {
                if (is_object($arg)) { $arg = 'CONVERTED OBJECT OF CLASS '.get_class($arg); }
            }
        }
        
        $trace_text[$i] = "#".$i." ".$call['file'].'('.$call['line'].') ';
        $trace_text[$i].= (!empty($call['object'])?$call['object'].$call['type']:'');
        $trace_text[$i].= $call['function'].'('.implode(', ',$call['args']).')';
    }
    
    var_dump($trace_text);
}

class A{
    public function test($obj){
        $obj->test();
    }
}

class B{
    public function test(){
        echo myPrint(debug_backtrace());
    }
}

$A = new A();
$B = new B();

$A->test($B);

?>

It should be noted that if an internal php function such as call_user_func in the backtrace, the 'file' and 'line' entries will not be set.

Most debug tracers will use these entries.  You should place a check to see if the key exists in the array before using this function.  Otherwise notices will be generated.

<?php

$arrTrace = debug_backtrace();

foreach ($arrTrace as $arr)
{
    if (!isset ($arr['file']))
    {
        $arr['file'] = '[PHP Kernel]';
    }

    if (!isset ($arr['line']))
    {
        $arr['line'] = '';
    }

    // Do something
}

?>

I wrote this function, in addition to jlim, for a nice NO-HTML output. 

Thee result has similarities to a Java-error. Hope you like it. 

(BTW, this function exits the script too, if debug_backtrace is displayed)
------------------------------
    function debug_bt()
    {
        if(!function_exists('debug_backtrace'))
        {
            echo 'function debug_backtrace does not exists'."\r\n";
            return;
        }
        //echo '<pre>';
        echo "\r\n".'----------------'."\r\n";
        echo 'Debug backtrace:'."\r\n";
        echo '----------------'."\r\n";
        foreach(debug_backtrace() as $t)
        {
            echo "\t" . '@ ';
            if(isset($t['file'])) echo basename($t['file']) . ':' . $t['line'];
            else
            {
                // if file was not set, I assumed the functioncall
                // was from PHP compiled source (ie XML-callbacks).
                echo '<PHP inner-code>';
            }

            echo ' -- ';

            if(isset($t['class'])) echo $t['class'] . $t['type'];

            echo $t['function'];

            if(isset($t['args']) && sizeof($t['args']) > 0) echo '(...)';
            else echo '()';

            echo "\r\n";
        }
        //echo '</pre>';
        exit;
         }

Here's my little updated contribution - it prints colorful output in the way I prefer.  Define a helper function isRootIp() that contains an array including your IP; then calls to bt() simply return, so you can sprinkle backtraces in live sites w/o anyone knowing.

<?php
function bt()
{
    if( ! isRootIp() )
    {
        return false;
    }
    array_walk( debug_backtrace(), create_function( '$a,$b', 'print "<br /><b>". basename( $a[\'file\'] ). "</b> &nbsp; <font color=\"red\">{$a[\'line\']}</font> &nbsp; <font color=\"green\">{$a[\'function\']} ()</font> &nbsp; -- ". dirname( $a[\'file\'] ). "/";' ) );
}
?>

Simple function to get a string in form "filename: [class->][function(): ]"

<?php
function get_caller_info() {
    $c = '';
    $file = '';
    $func = '';
    $class = '';
    $trace = debug_backtrace();
    if (isset($trace[2])) {
        $file = $trace[1]['file'];
        $func = $trace[2]['function'];
        if ((substr($func, 0, 7) == 'include') || (substr($func, 0, 7) == 'require')) {
            $func = '';
        }
    } else if (isset($trace[1])) {
        $file = $trace[1]['file'];
        $func = '';
    }
    if (isset($trace[3]['class'])) {
        $class = $trace[3]['class'];
        $func = $trace[3]['function'];
        $file = $trace[2]['file'];
    } else if (isset($trace[2]['class'])) {
        $class = $trace[2]['class'];
        $func = $trace[2]['function'];
        $file = $trace[1]['file'];
    }
    if ($file != '') $file = basename($file);
    $c = $file . ": ";
    $c .= ($class != '') ? ":" . $class . "->" : "";
    $c .= ($func != '') ? $func . "(): " : "";
    return($c);
}
?>

Usage like:

<?php
function debug($str) {
    echo get_caller_info() . $str . "<br>\n";
}
?>

get_caller_info() will return info about the function /class->method that called debug().

Howdy guys, just a note really - The ['args'] data within the resulting array is supplied by reference. I found myself editing the reference unknowingly which in turn shows its ugly head further down the line if you call multiple backtrace.

<?php
$trace = array_reverse(debug_backtrace());

// LOOP BACKTRACE
$la = 0;
$lb = count($trace);
while ($la<$lb){

    // DATA FROM BACKTRACE
    $trace[$la]['file'];
    $trace[$la]['line'];
    $trace[$la]['args'];
    $trace[$la]['function'];
    // DATA FROM BACKTRACE

    // LOOP ARGUMENTS ARRAY
    $ba = 0;
    $bb = count($trace[$la]['args']);
    while ($ba<$bb){

        $trace[$la]['args'][$ba] = "EDITING A REFERENCE/POINTER";

        $ba++;
    }
    unset($bb);
    unset($ba);
    // LOOP ARGUMENTS ARRAY

    $la++;
}
unset($lb);
unset($la);
// LOOP BACKTRACE
?>

When using debug_backtrace() to check if you're being accessed from another caller, please remember to ask debug_backtrace to only go as far as needed in depth and skip taking the entire debug object as return parameter:

<?php
    if (count(debug_backtrace(FALSE, 1)) == 0)
    {
        // Do something
    }
?>

It works a little bit different with resources in different PHP versions.

For example:
function foo($bar)
{
  return debug_backtrace();
}

$resource = fopen(__FILE__, 'r');
$backtrace = foo($resource);
echo "when resource is opened: " . gettype($backtrace[0]['args'][0]) . "\n";
fclose($resource);
echo "when resource is closed: " . gettype($backtrace[0]['args'][0]) . "\n";

With 5.3.10 I got:
when resource is opened: resource
when resource is closed: resource

With 5.5.9:
when resource is opened: resource
when resource is closed: unknown type

Be carefull.

<?
// useful and comfortable debug function
// it's show memory usage and time flow between calls, so we can quickly find a block of code that need optimisation...
// example result:
/*
debug example.php> initialize
debug example.php> code-lines: 39-41 time: 2.0002 mem: 19 KB
debug example.php> code-lines: 41-44 time: 0.0000 mem: 19 KB
debug example.php> code-lines: 44-51 time: 0.6343 mem: 9117 KB
debug example.php> code-lines: 51-53 time: 0.1003 mem: 9117 KB
debug example.php> code-lines: 53-55 time: 0.0595 mem: 49 KB
 */

function debug()
{
   static $start_time = NULL;
   static $start_code_line = 0;

   $call_info = array_shift( debug_backtrace() );
   $code_line = $call_info['line'];
   $file = array_pop( explode('/', $call_info['file']));

   if( $start_time === NULL )
   {
       print "debug ".$file."> initialize\n";
       $start_time = time() + microtime();
       $start_code_line = $code_line;
       return 0;
   }

   printf("debug %s> code-lines: %d-%d time: %.4f mem: %d KB\n", $file, $start_code_line, $code_line, (time() + microtime() - $start_time), ceil( memory_get_usage()/1024));
   $start_time = time() + microtime();
   $start_code_line = $code_line;
}

////////////////////////////////////////////////
// example:

debug();
sleep(2);
debug();
// soft-code...
$a = 3 + 5;
debug();

// hard-code
for( $i=0; $i<100000; $i++)
{
    $dummy['alamakota'.$i] = 'alamakota'.$i;
}
debug();
usleep(100000);
debug();
unset($dummy);
debug();

?>

I've started creating an external debug server for PHP. A PHP app require_once's a TADebugger(), which communicates with the debug sever. Find the OS X universal binary here [PHP source sample included]:

   http://www.turingart.com/downloads/phpDebugger.zip

Currently, TADebugger allows to post these properties back to the debug server:

- Call backtraces
- String messages
- Source files, which were referenced by a backtrace call

Note, that the binary is a early version.

Surprizingly, debug_backtrace() cannot aquire arguments from the function that is used as the second or later argument of a function.

<?php

function a($p) {
    $backtrace = debug_backtrace();
    
    if (isset($backtrace[0]['args']))
        var_export($backtrace[0]['args']);
    else
        echo "Cannot aquire arguments";
    echo "<br />";
    
    return $p;
}

function b($p1, $p2, $p3) {
    echo "$p1, $p2, $p3";
}

// This outputs:
//    array ( 0 => 'First a', )
//    Cannot aquire arguments
//    Cannot aquire arguments
//    First a, Second a, Third a
b(a("First a"), a("Second a"), a("Third a"));

?>

I want to point out that debug_backtrace() in new versions of php can detect recursion // circular references .. avoiding memory consumption.

Example:

<?php

class ParentClass {
        public function __construct() 
        {
                $this->_child = new ChildClass($this);
                var_dump(debug_backtrace());
        }
}

class ChildClass {
        public function __construct(ParentClass $p)
        {
                $this->_parent = $p;
        }
}

$test = new ParentClass();
?>

Output:

array(1) {
  [0]=>
  array(7) {
    ["file"]=>
    string(23) "/home/jcm/testdebug.php"
    ["line"]=>
    int(18)
    ["function"]=>
    string(11) "__construct"
    ["class"]=>
    string(11) "ParentClass"
    ["object"]=>
    object(ParentClass)#1 (1) {
      ["_child"]=>
      object(ChildClass)#2 (1) {
        ["_parent"]=>
        *RECURSION*
      }
    }
    ["type"]=>
    string(2) "->"
    ["args"]=>
    array(0) {
    }
  }
}

Attention in the *RECURSION* hint provided

One line of code to print simplest and shortest human readable backtrace:)
<?php
array_walk(debug_backtrace(),create_function('$a,$b','print "{$a[\'function\']}()(".basename($a[\'file\']).":{$a[\'line\']}); ";'));
?>

A usual entry looks like this:
<?php
array(6) {
  'file' =>
  string(87) "DbSelector.php"
  'line' =>
  int(171)
  'function' =>
  string(5) "error"
  'class' =>
  string(42) "LoggingService"
  'type' =>
  string(2) "::"
  'args' =>
  array(1) {
    [0] =>
    string(27) "Connecting to DB: unittests"
  }
}
?>

Be warned though that 'file' and 'class' do not reference the same thing!
'file' means which file calls the next step.
'class' is the next step being called.

So 'file' is the caller, 'class' is the callee.

I use this simple but effective function so i can see which method in the child class called the current method (in the parent class).

<?php
function get_caller_method()
{
    $traces = debug_backtrace();

    if (isset($traces[2]))
    {
        return $traces[2]['function'];
    }

    return null;
}
?>

Another variation formatting backtrace.
Parameter $ignore to ignore the extra calls.
<?php
/**
 * Getting backtrace
 *
 * @param int $ignore ignore calls
 *
 * @return string
 */
protected function getBacktrace($ignore = 2)
{
    $trace = '';
    foreach (debug_backtrace() as $k => $v) {
        if ($k < $ignore) {
            continue;
        }

        array_walk($v['args'], function (&$item, $key) {
            $item = var_export($item, true);
        });

        $trace .= '#' . ($k - $ignore) . ' ' . $v['file'] . '(' . $v['line'] . '): ' . (isset($v['class']) ? $v['class'] . '->' : '') . $v['function'] . '(' . implode(', ', $v['args']) . ')' . "\n";
    }

    return $trace;
}
?>

need no Xdebug or dbg.so on server, return more detailed message:

diyism_trace.php:
<?php
define(TRACES_MODE, 'TEXTAREA');//'TEXTAREA' or 'FIREPHP'
$GLOBALS['traces.pre']=array();
function my_array_diff($arr1, $arr2)
         {foreach ($arr1 as $k=>$v)
                  {if (in_array($v, $arr2, true))
                      {unset($arr1[$k]);
                      }
                  }
          return $arr1;
         }
function my_var_export($var, $is_str=false)
         {$rtn=preg_replace(array('/Array\s+\(/', '/\[(\d+)\] => (.*)\n/', '/\[([^\d].*)\] => (.*)\n/'), array('array (', '\1 => \'\2\''."\n", '\'\1\' => \'\2\''."\n"), substr(print_r($var, true), 0, -1));
          $rtn=strtr($rtn, array("=> 'array ('"=>'=> array ('));
          $rtn=strtr($rtn, array(")\n\n"=>")\n"));
          $rtn=strtr($rtn, array("'\n"=>"',\n", ")\n"=>"),\n"));
          $rtn=preg_replace(array('/\n +/e'), array('strtr(\'\0\', array(\'    \'=>\'  \'))'), $rtn);
          $rtn=strtr($rtn, array(" Object',"=>" Object'<-"));
          if ($is_str)
             {return $rtn;
             }
          else
              {echo $rtn;
              }
         }
function tick_handler()
         {$tmp=debug_backtrace();
          $trace=my_array_diff($tmp, $GLOBALS['traces.pre']);
          //echo '<pre>';var_export($trace);echo '</pre>';echo '<br/>'; //for debug diyism_trace.php
          $trace=array_values($trace);
          $GLOBALS['traces.pre']=$tmp;
          if (count($trace)>0 && $trace[0]['file'].'/'.@$tmp[1]['function']!==@$GLOBALS['traces'][count($GLOBALS['traces'])-1]['key']) //filter empty array and rearrange array_values(), because some lines will trigger two tick events per line, for example: 1.last line is "some code;questmark>" 2.error_reporting(...
             {for ($i=count($trace)-1; $i>=0; --$i)
                  {$GLOBALS['traces'][]=$tmp_fb=array_merge(array('key'=>$trace[$i]['file'].'/'.@$tmp[$i+1]['function']), $trace[$i], array('function'=>strtr($trace[$i]['function'], array('tick_handler'=>'CONTINUE')), 'in_function'=>@$tmp[$i+1]['function']));
                   TRACES_MODE==='FIREPHP'?fb(trace_output($tmp_fb), 'diyism_trace:'.++$GLOBALS['diyism_trace_no']):'';
                  }
             }
         }
function trace_output($trace)
         {$trace['in_function']=strtr(@$trace['in_function'], array('require'=>'', 'require_once'=>'', 'include'=>'', 'include_once'=>''));
          $trace['args']=$trace['args']?strtr(preg_replace(array('/\n +/'), array(''), preg_replace(array('/\n  \d+ => /'), array(''), substr(my_var_export($trace['args'], true), 7, -3))), array("\r"=>'\r', "\n"=>'\n')):'';
          return $trace['file'].($trace['in_function']?'/'.$trace['in_function'].'()':'').'/'.$trace['line'].': '.$trace['function'].'('.$trace['args'].')';
         }
function traces_output()
         {echo '<textarea style="width:100%;height:300px;">';
          $GLOBALS['traces']=array_slice($GLOBALS['traces'], 2);//remove registering tick line and requiring 'diyism_trace.php' line
          foreach ($GLOBALS['traces'] as $k=>$trace)
                  {echo htmlentities($k.':'.trace_output($trace)."\n");
                  }
          echo '</textarea>';
         }
register_tick_function('tick_handler');
TRACES_MODE==='TEXTAREA'?register_shutdown_function('traces_output'):'';
?>

test.php:
<?php
declare(ticks=1);
require 'diyism_trace.php';

a('a', array('hello'));
1+2;
b();
function a()
         {$d=1;
          b();
          $d=2;
         }
function b()
         {1+1;
         }
?>

Options provided by bitmask parameters can be disabled using !

<?php
debug_backtrace( !DEBUG_BACKTRACE_PROVIDE_OBJECT | DEBUG_BACKTRACE_IGNORE_ARGS);
?>

The `args` element contains only the arguments actually passed to the function or method.  It does not include default parameters if they were not explicitly specified.  (A least, this is the case with PHP 7.1.9.)  This is consistent with the behaviour of `func_get_args()`.

Surprisingly, no one has described one of the best uses of this: dumping a variable and showing the location. When debugging, especially a big and unfamiliar system, it's a pain remembering where I added those var dumps. Also, this way there is a separator between multiple dump calls.

<?php

function dump( $var ) {
    $result = var_export( $var, true );
    $loc = whereCalled();
    return "\n<pre>Dump: $loc\n$result</pre>";
}

function whereCalled( $level = 1 ) {
    $trace = debug_backtrace();
    $file   = $trace[$level]['file'];
    $line   = $trace[$level]['line'];
    $object = $trace[$level]['object'];
    if (is_object($object)) { $object = get_class($object); }

    return "Where called: line $line of $object \n(in $file)";
}
?>

In addition, calling 'whereCalled()' from any function will quickly identify locations that are doing something unexpected (e.g., updating a property at the wrong time). I'm new to PHP, but have used the equivalent in Perl for years.

Here is a function to cleanly output the debug_backtrace to the error_log

<?php
/*
 * Send the output from a backtrace to the error_log
 * @param string $message Optional message that will be sent the the error_log before the backtrace
 */
function log_trace($message = '') {
    $trace = debug_backtrace();
    if ($message) {
        error_log($message);
    }
    $caller = array_shift($trace);
    $function_name = $caller['function'];
    error_log(sprintf('%s: Called from %s:%s', $function_name, $caller['file'], $caller['line']));
    foreach ($trace as $entry_id => $entry) {
        $entry['file'] = $entry['file'] ? : '-';
        $entry['line'] = $entry['line'] ? : '-';
        if (empty($entry['class'])) {
            error_log(sprintf('%s %3s. %s() %s:%s', $function_name, $entry_id + 1, $entry['function'], $entry['file'], $entry['line']));
        } else {
            error_log(sprintf('%s %3s. %s->%s() %s:%s', $function_name, $entry_id + 1, $entry['class'], $entry['function'], $entry['file'], $entry['line']));
        }
    }
}
?>

Further to my previous note, the 'object' element of the array can be used to get the parent object.  So changing the get_class_static() function to the following will make the code behave as expected:

<?php
    function get_class_static() {
        $bt = debug_backtrace();
    
        if (isset($bt[1]['object']))
            return get_class($bt[1]['object']);
        else
            return $bt[1]['class'];
    }
?>

HOWEVER, it still fails when being called statically.  Changing the last two lines of my previous example to

<?php
  foo::printClassName();
  bar::printClassName();
?>

...still gives the same problematic result in PHP5, but in this case the 'object' property is not set, so that technique is unavailable.

Everybody seems to have their favorite use.  I substitute this function for die().  It gives a message 
to the user and emails me a PrettyPrint of what went wrong.  $info is set by me, 
and it does a special check in the database object.

<?php
// var_format

function var_format($v) // pretty-print var_export
{
    return (str_replace(array("\n"," ","array"),
array("<br>","&nbsp;","&nbsp;<i>array</i>"),
var_export($v,true))."<br>");
}
function myDie($info) 
{
    $mysqlerr=strpos($info,"ERROR=You have an error in your SQL syntax");
    if($mysqlerr>0)$info=substr($info,0,$mysqlerr)." mySql format error";
    $out="<br>MSG='$info'<br>".var_format($_REQUEST)."<br>";
    $bt=debug_backtrace();
    $sp=0;
    $trace="";
    foreach($bt as $k=>$v)
    {
        extract($v);
        $file=substr($file,1+strrpos($file,"/"));
        if($file=="db.php")continue; // the db object
        $trace.=str_repeat("&nbsp;",++$sp); //spaces(++$sp);
        $trace.="file=$file, line=$line, function=$function<br>";        
    } 
    $out.="<br>".backTrace();
    if(substr($info,0,4)=="XXX ") // special errrors when db is inaccessible
    {
        $out=str_replace("<br>","\n",$out);
        $out=str_replace("&nbsp;"," ",$out);
        mail("[email protected]","Database Execution Error for user ".$REMOTE_ADDR,"$out");
        exit("Database Access Error. Please try again later.");
    }
    mail("[email protected]",'Error Monitor','Execution Error',$out);
    exit("DANG! An execution error in the program has been sent to the webmaster. 
If you don't get an email from him soon, please call him.");
}
?>

This produces an output like this

 file=badmode.php, line=5, function=backTrace
  file=login.php, line=209, function=require
   file=midScreen.php, line=264, function=require
    file=masterindex.php, line=161, function=require
     file=production2.php, line=121, function=require
      file=index.php, line=16, function=require

Here is my simple example:
Code printing variable of class which instatiates the printing class.

Well, I am sure you understand when looking at the code:
Print result is: jippii

<?php
class A {

        function something() {
                $s = debug_backtrace();
                
                $callingObject = $s[1]['object']; 
                $test = $callingObject->jip;
                print $test;
        }

}

class B {
      var $jip; 
      
        function execute() {
                $a = new A();
                $this->jip = "jippii";  
                $a->something(); 
        }

}
$control = new B();
$control->execute();
?>

Here's a way to get the arguments for an upstream function in your stack (works with class methods, static methods and non-class methods):
<?php
/**
 * getArgs - find arguments of upstream method
 * can be called with, e.g. "funcname", "class::staticmethod", "class->instancemethod".
 */
function getArgs( $target, $subclass_ok = true ) {

    if( strpos( $target, "::" ) ) {
        list( $class, $target ) = explode( "::", $target, 2 );
        $type = "::";
    }
    else if( strpos( $target, "->" ) ) {
        list( $class, $target ) = explode( "->", $target, 2 );
        $type = "->";
    }
    else {
        $type = NULL;
        $class = NULL;
    }
    $class and $class = new ReflectionClass( $class );

    foreach( debug_backtrace() as $obj ) {

        if( $obj['function'] == $target ) {
            if( $type and $obj['type'] == $type ) {
                $_cl = new ReflectionClass( $obj['class'] );
                if( $_cl->getName() == $class->getName() or ( $subclass_ok and $_cl->isSubclassOf( $class ) ) ) {
                    return $obj['args'];
                }
                unset( $_cl );
            }
            else if( !$type ) {
                return $obj['args'];
            }
        }

    }

    return NULL;

}
?>

Some example usage:
<?php
class Foo {
    function test() {
        $args = getArgs( "Foo->base" );
        print( "the parameter 'v' to my call of base was: {$args[0]}\n" );
    }
    function base( $v ) {
        $this->test();
    }
}

$f = new Foo();
$f->base( 713 ); // will print.. ".. my call of base was: 713"

?>

Trust me, there are some reasons for why you might want to do this :)

A simple python-like backtrace. Note that I don't recurse into arrays if they are passed as arguments to functions.

function backtrace()
{
    $bt = debug_backtrace();
    
    echo("<br /><br />Backtrace (most recent call last):<br /><br />\n");    
    for($i = 0; $i <= count($bt) - 1; $i++)
    {
        if(!isset($bt[$i]["file"]))
            echo("[PHP core called function]<br />");
        else
            echo("File: ".$bt[$i]["file"]."<br />");
        
        if(isset($bt[$i]["line"]))
            echo("&nbsp;&nbsp;&nbsp;&nbsp;line ".$bt[$i]["line"]."<br />");
        echo("&nbsp;&nbsp;&nbsp;&nbsp;function called: ".$bt[$i]["function"]);
        
        if($bt[$i]["args"])
        {
            echo("<br />&nbsp;&nbsp;&nbsp;&nbsp;args: ");
            for($j = 0; $j <= count($bt[$i]["args"]) - 1; $j++)
            {
                if(is_array($bt[$i]["args"][$j]))
                {
                    print_r($bt[$i]["args"][$j]);
                }
                else
                    echo($bt[$i]["args"][$j]);    
                            
                if($j != count($bt[$i]["args"]) - 1)
                    echo(", ");
            }
        }
        echo("<br /><br />");
    }
}

Hi, I got tired of using a trace( $message, __FILE__, __LINE__ ) function I made.  It forced me to include the file and line params (since php doesn't have macros) so I decided to make an alternative.

Simply call this new version using trace( 'my message' ); and it prints out a stack trace in a clearer way than the one stored in the debug_backtrace() array.  It handles traces from outside of functions, traces in nested functions, and traces in included files, and also displays the function in a way that can be pasted right back into your php code for faster testing!

NOTE - be sure to save your files with the correct line endings for the line numbers to work correctly, which for Mac OS X is unix.  You can get to this option in the popup menu in the toolbar at the top of each window in BBEdit.

<?php

function    print_var( $var )
{
   if( is_string( $var ) )
       return( '"'.str_replace( array("\x00", "\x0a", "\x0d", "\x1a", "\x09"), array('\0', '\n', '\r', '\Z', '\t'), $var ).'"' );
   else if( is_bool( $var ) )
   {
       if( $var )
           return( 'true' );
       else
           return( 'false' );
   }
   else if( is_array( $var ) )
   {
       $result = 'array( ';
       $comma = '';
       foreach( $var as $key => $val )
       {
           $result .= $comma.print_var( $key ).' => '.print_var( $val );
           $comma = ', ';
       }
       $result .= ' )';
       return( $result );
   }
   
   return( var_export( $var, true ) );    // anything else, just let php try to print it
}

function    trace( $msg )
{
   echo "<pre>\n";
   
   //var_export( debug_backtrace() ); echo "</pre>\n"; return;    // this line shows what is going on underneath
   
   $trace = array_reverse( debug_backtrace() );
   $indent = '';
   $func = '';
   
   echo $msg."\n";
   
   foreach( $trace as $val)
   {
       echo $indent.$val['file'].' on line '.$val['line'];
       
       if( $func ) echo ' in function '.$func;
       
       if( $val['function'] == 'include' ||
           $val['function'] == 'require' ||
           $val['function'] == 'include_once' ||
           $val['function'] == 'require_once' )
           $func = '';
       else
       {
           $func = $val['function'].'(';
           
           if( isset( $val['args'][0] ) )
           {
               $func .= ' ';
               $comma = '';
               foreach( $val['args'] as $val )
               {
                   $func .= $comma.print_var( $val );
                   $comma = ', ';
               }
               $func .= ' ';
           }
           
           $func .= ')';
       }
       
       echo "\n";
       
       $indent .= "\t";
   }
   
   echo "</pre>\n";
}

trace( 'error outside function' );

function    test( $param1, $param2, $param3, $param4 )
{
   trace( 'error in test()' );
}

test( 1.1, "param2\n", array( 1 => "a\n", "b\n" => 2 ), false );

?>

Pretty print the backtrace(). Functions are indented based on call value, and file is linked using file:// for convenience. 

Enjoy, John Lim

    function adodb_backtrace($print=true)
    {
        $s = '';
        if (PHPVERSION() >= 4.3) {
        
            $MAXSTRLEN = 64;
        
            $s = '<pre align=left>';
            $traceArr = debug_backtrace();
            array_shift($traceArr);
            $tabs = sizeof($traceArr)-1;
            foreach ($traceArr as $arr) {
                for ($i=0; $i < $tabs; $i++) $s .= ' &nbsp; ';
                $tabs -= 1;
                $s .= '<font face="Courier New,Courier">';
                if (isset($arr['class'])) $s .= $arr['class'].'.';
                foreach($arr['args'] as $v) {
                    if (is_null($v)) $args[] = 'null';
                    else if (is_array($v)) $args[] = 'Array['.sizeof($v).']';
                    else if (is_object($v)) $args[] = 'Object:'.get_class($v);
                    else if (is_bool($v)) $args[] = $v ? 'true' : 'false';
                    else { 
                        $v = (string) @$v;
                        $str = htmlspecialchars(substr($v,0,$MAXSTRLEN));
                        if (strlen($v) > $MAXSTRLEN) $str .= '...';
                        $args[] = $str;
                    }
                }
                
                $s .= $arr['function'].'('.implode(', ',$args).')';
                $s .= sprintf("</font><font color=#808080 size=-1> # line %4d,".
  " file: <a href=\"file:/%s\">%s</a></font>",
  $arr['line'],$arr['file'],$arr['file']);
                $s .= "\n";
            }    
            $s .= '</pre>';
            if ($print) print $s;
        }
        return $s;
    }

ATTN: jlim#natsoft.com.my

Great function, but you have a few bugs.

At the line: 
foreach($arr['args'] as $v)

Change it to:
$args = array();
if(!empty($arr['args'])) foreach($arr['args'] as $v)

And since line & file are not present in the array if calling from the error handler,

$Line = (isset($arr['line'])? $arr['line'] : "unknown");
$File = (isset($arr['file'])? $arr['file'] : "unknown");

and substitute accordingly.

Here's my version of it, alas with different formatting:
----------------------------------------

function DBG_GetBacktrace()
{
    $s = '';
    $MAXSTRLEN = 64;
    
    $s = '<pre align=left>';
    $traceArr = debug_backtrace();
    array_shift($traceArr);
    $tabs = sizeof($traceArr)-1;
    foreach($traceArr as $arr)
    {
        for ($i=0; $i < $tabs; $i++) $s .= ' &nbsp; ';
        $tabs -= 1;
        $s .= '<font face="Courier New,Courier">';
        if (isset($arr['class'])) $s .= $arr['class'].'.';
        $args = array();
        if(!empty($arr['args'])) foreach($arr['args'] as $v)
        {
            if (is_null($v)) $args[] = 'null';
            else if (is_array($v)) $args[] = 'Array['.sizeof($v).']';
            else if (is_object($v)) $args[] = 'Object:'.get_class($v);
            else if (is_bool($v)) $args[] = $v ? 'true' : 'false';
            else
            { 
                $v = (string) @$v;
                $str = htmlspecialchars(substr($v,0,$MAXSTRLEN));
                if (strlen($v) > $MAXSTRLEN) $str .= '...';
                $args[] = "\"".$str."\"";
            }
        }
        $s .= $arr['function'].'('.implode(', ',$args).')</font>';
        $Line = (isset($arr['line'])? $arr['line'] : "unknown");
        $File = (isset($arr['file'])? $arr['file'] : "unknown");
        $s .= sprintf("<font color=#808080 size=-1> # line %4d, file: <a href=\"file:/%s\">%s</a></font>",
            $Line, $File, $File);
        $s .= "\n";
    }    
    $s .= '</pre>';
    return $s;
}

I find it useful to know if a function is being called. in Java for instance you usually print a line with the functionname and arguments in the beginning of the function. I wanted to achieve the same thing in php thus i wrote the following class:

<?php
class Debug 
{
    private static $calls;

    public static function log($message = null)
    {
        if(!is_array(self::$calls))
            self::$calls = array();

        $call = debug_backtrace(false);
        $call = (isset($call[1]))?$call[1]:$call[0];

        $call['message'] = $message;
        array_push(self::$calls, $call);
    }
}
?>

include this class before anything else
usage: Debug::log($message); at the beginning of your function.

write yourself a nice printout of the data;

A function that i use for debug
I shortened variables name and i eliminated the spaces from second function in order fit in post :(

<?php
define("LFP", './lt.log');
function LogTrace($Argument, $lfn = LFP, $itw = '  ')
{
    error_log("=====\r", 3, $lfn); 
    error_log("[BEGIN BACKTRACE]\r", 3, $lfn); 
    $it = '';
    $Ts = array_reverse(debug_backtrace());
    foreach($Ts as $T)
       {  
        if($T['function'] != 'include' && $T['function'] != 'require' && $T['function'] != 'include_once' && $T['function'] != 'require_once')
        {
            $ft = $it . '<'. basename($T['file']) . '> on line ' . $T['line'];  
            if($T['function'] != 'LogTrace')
            {
                if(isset($T['class']))
                    $ft .= ' in method ' . $T['class'] . $T['type'];
                else 
                    $ft .= ' in function ';
                $ft .= $Trace['function'] . '(';
            }
            else
                $ft .= '(';
            if(isset($T['args'][0]))
            {
                if($T['function'] != 'LogTrace')
                {
                    $ct = '';
                    foreach($T['args'] as $A)
                    {
                        $ft .= $ct . LogVar($A, '', $it, $itw, 0);
                        $ct = $it . $itw . ',';
                    }
                }
                else
                    $ft .= LogVar($T['args'][0], '', $it, $itw, 0);
            }
            $ft .= $it . ")\r";
            error_log($ft, 3, $lfn); 
            $it .= $itw;
        }            
    }
    error_log("[END BACKTRACE]\r", 3, $lfn);
}

function LogVar(&$Var, $vn, $pit, $itw, $nlvl, $m = '')
{
    if($nlvl>=16) return;
    if($nlvl==0){$tv=serialize($Var);$tv=unserialize($tv);}
    else $tv=&$Var; 
    $it=$pit.$itw;
    for($i=0; $i<$nlvl;$i++) $it.='.'.$itw;
    $o='';$nl="\n";
    if(is_array($tv))
    {
        if(strlen($vn)>0) $o.=$it.$m.'<array> $'.$vn.' = (';
        else $o.="\r".$it.$m.'<array> = (';
        $o.= $nl;$AK=array_keys($tv);
        foreach($AK as $AN) {$AV=&$tv[$AN];$o.=LogVar($AV,$AN,$pit,$itw,$nlvl+1);}
        $o.=$it.')'.$nl;
    }
    else if(is_string($tv))
    {
        if(strlen($vn)>0)$o.=$it.$m.'<string> $'.$vn.' = ';
        else $o.=' '.$m.'<string> = ';
        if($tv===null) $o.='NULL';
        else $o.='"'.$tv.'"';
        $o.=$nl;
    }
    else if(is_bool($tv))
    {
        if(strlen($vn) > 0) $o.=$it.$m.'<boolean> $'.$vn.' = ';
        else $o.=' '.$m.'<boolean> = ';
        if($tv===true) $o.='TRUE';
        else $o.='FALSE';
        $o.=$nl;
    }
    else if(is_object($tv))
    {
        if(strlen($vn)>0)
        {
            $o.=$pit.$itw;
            for($i=0;$i<$nlvl;$i++) $o.='.'.$itw;
            $o.=$m.'<'.get_class($tv).'::$'.$vn.'> = {'.$nl;
        }
        else $o.=' '.$m.'<'.get_class($tv).'::> = {'.$nl;
        $R=new ReflectionClass($tv);
        $o.=$it.'.'.$itw.'Class methods {'.$nl;
        $CM=$R->getMethods();
        foreach($CM as $MN => $MV)
        {
            $o.=$it.'.'.$itw.'.'.$itw.implode(' ',Reflection::getModifierNames($MV->getModifiers())).' '.$MV->getName().'(';
            $MP=$MV->getParameters(); $ct='';
            foreach($MP as $MPN => $MPV)
            {
                $o.=$ct; $o.=$MPV->isOptional()?'[':'';
                if($MPV->isArray()) $o.='<array> ';
                else if($MPV->getClass()!==null) $o.='<'.$MPV->getClass()->getName().'::> ';
                $o.=$MPV->isPassedByReference()?'&':''; $o.='$'.$MPV->getName();
                if($MPV->isDefaultValueAvailable())
                 {
                    if($MPV->getDefaultValue()===null) $o.=' = NULL';
                    else if($MPV->getDefaultValue()===true) $o.=' = TRUE';
                    else if($MPV->getDefaultValue()===false) $o.=' = FALSE';    
                    else $o.=' = '.$MPV->getDefaultValue();    
                }
                $o.=$MPV->isOptional()?']':''; $ct=', ';
            }
            $o.=')'.$nl;
        }
        $o.=$it.'.'.$itw.'}'.$nl; $o.=$it.'.'.$itw.'Class properties {'.$nl;
        $CV=$R->getProperties();
        foreach($CV as $CN => $CV)
        {
            $M=implode(' ',Reflection::getModifierNames($CV->getModifiers())).' ';
            $CV->setAccessible(true); 
            $o.=LogVar($CV->getValue($tv),$CV->getName(),$pit,$itw,$nlvl+2,$M);
        }
        $o.=$it.'.'.$itw.'}'.$nl; $o.=$it.'.'.$itw.'Object variables {'.$nl;
         $OVs=get_object_vars($tv);    
        foreach($OVs as $ON => $OV) $o.=LogVar($OV,$ON,$pit,$itw,$nlvl+2);
        $o.=$it.'.'.$itw.'}'.$nl; $o.=$pit.$itw;
        for($i=0;$i<$nlvl;$i++)    $o.='.'.$itw;
        $o.='}'.$nl;
    }
    else
    {
        if(strlen($vn)>0) $o.=$it.$m.'<'.gettype($tv).'> $'.$vn.' = '.$tv;
        else $o.=' '.$m.'<'.gettype($tv).'> = '.$tv;
        $o.=$nl;
    }          
    return $o;    
}
//test
date_default_timezone_set('Europe/Bucharest');
$date = new DateTime('2010-01-28');
LogTrace($date); 
?>

An easy function to pull all details of the debug backtrace:

<?php
function getDebugBacktrace($NL = "<BR>") {
    $dbgTrace = debug_backtrace();
    $dbgMsg .= $NL."Debug backtrace begin:$NL";
    foreach($dbgTrace as $dbgIndex => $dbgInfo) {
        $dbgMsg .= "\t at $dbgIndex  ".$dbgInfo['file']." (line {$dbgInfo['line']}) -> {$dbgInfo['function']}(".join(",",$dbgInfo['args'])")$NL";
    }
    $dbgMsg .= "Debug backtrace end".$NL;
    return $dbgMsg;
}
?>

Then you can call it anywhere you want to get a string with the debug backtrace in readable format (i.e. your error handling function)

<?php
$backtrace = getDebugBacktrace();
echo "Fatal error! Cannot connect to database!";
echo $backtrace;
?>

If you're running on command line, you might want to replace the line split. You can do that thru the function argument:

<?php
$backtrace = getDebugBacktrace("\n");
echo "Error! Server is running out of foos! Dumping error backtrace";
echo $backtrace;
?>

Hope that helps,
Aryel