php调试利器debug_print_backtrace()

<?php 
class a{ 
function say($msg) { 
echo "msg:".$msg; 
echo "<pre>";debug_print_backtrace(); 
} 
} 

class b { 
function say($msg) { 
$a = new a(); 
$a->say($msg); 
} 
} 

class c { 
function __construct($msg) { 
$b = new b(); 
$b->say($msg); 
} 
} 

$c = new c("test"); 

msg:test 
#0 a->say(test) called at [/var/www/test/test0723.php:12] 
#1 b->say(test) called at [/var/www/test/test0723.php:19] 
#2 c->__construct(test) called at [/var/www/test/test0723.php:23]