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]