What the debug_backtrace() exactly works in php?

Question

While working on one of my PHP project I got a function debug_backtrace() at the start of code file as <?php debug_backtrace() || die ("Direct access not permitted"); ?> <?php debug_backtrace() || die ("Direct access not permitted"); ?> <?php debug_backtrace() || die ("Direct access not permitted"); ?> .

While studding on it I got some explanation that it works as:

Debugging PHP issues in a Drupal website can be anything from quick and easy to seriously problematic. PHP includes a debugging function called debug_backtrace , which will print out the chain of code that leads up to the point where the backtrace function is called.

And When I use var_dump() with debug_backtrace() I got following result:

array(2) {
  [0]=>
  array(3) {
    ["file"]=>
    string(61) "C:\xampp\htdocs\folder_name\templates\default\models\home.php"
    ["line"]=>
    int(30)
    ["function"]=>
    string(7) "include"
  }
  [1]=>
  array(4) {
    ["file"]=>
    string(37) "C:\xampp\htdocs\folder_name\index.php"
    ["line"]=>
    int(146)
    ["args"]=>
    array(1) {
      [0]=>
      string(61) "C:\xampp\htdocs\folder_name\templates\default\models\home.php"
    }
    ["function"]=>
    string(7) "include"
  }
}

I didn't get that what debug_backtrace() function exactly work.

Please anyone explain is welcome. Thanks in advance.

Studied links:

debug_backtrace() from registered shutdown function in PHP

Debugging PHP Code with debug_backtrace

Assign debug_backtrace() To a variable in PHP

Print PHP Call Stack

How can I save a PHP backtrace to the error log?

Answer 1

Giving a basic example...

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

echo "Start...";
print_r(debug_backtrace());

function t1 ()  {
    echo "Start t1...";
    print_r(debug_backtrace());

}

function t2()   {
    echo "Start t2...";
    print_r(debug_backtrace());
    t1();
}

echo "before calls...";
print_r(debug_backtrace());
t1();
t2();

Will output...

Start...Array
(
)
before calls...Array
(
)
Start t1...Array
(
    [0] => Array
        (
            [file] => /home/nigel/workspace/PHPTest/TestSource/part3.php
            [line] => 22
            [function] => t1
            [args] => Array
                (
                )

        )

)
Start t2...Array
(
    [0] => Array
        (
            [file] => /home/nigel/workspace/PHPTest/TestSource/part3.php
            [line] => 23
            [function] => t2
            [args] => Array
                (
                )

        )

)
Start t1...Array
(
    [0] => Array
        (
            [file] => /home/nigel/workspace/PHPTest/TestSource/part3.php
            [line] => 17
            [function] => t1
            [args] => Array
                (
                )

        )

    [1] => Array
        (
            [file] => /home/nigel/workspace/PHPTest/TestSource/part3.php
            [line] => 23
            [function] => t2
            [args] => Array
                (
                )

        )

)

I hope this shows that all the debug_backtrace function does is return what has been called so far. So when you first call t1 , it is simply a stack trace of the call to t1 . The same for the start of t2 , but when t2 calls t1 , the trace lists the call to t2 and t1 .

But also as you can see, that debug_backtrace from Start.. shows nothing, as there are no levels of code that have caused this trace to be printed.

In your case it calls debug_backtrace and uses the or die() to say 'if debug_backtrace returns nothing, then die() '

Answer 2

I think the most useful method for debug_backtrace() is to trace which file is the init one start the core, example like

a.php
include 'b.php';

b.php
function test(){
     echo('whatever');
}
print_r(debug_backtrace())

php a.php


whateverArray
(
    [0] => Array
        (
            [file] => /opt/php/b.php
            [line] => 7
            [function] => test
            [args] => Array
                (
                )

        )

    [1] => Array
        (
            [file] => /opt/php/a.php
            [line] => 3
            [args] => Array
                (
                    [0] => /opt/php/b.php
                )

            [function] => include
        )

)

So, you can get from

$backtrace = debug_backtrace()
echo $backtrace[count($backtrace) - 1]['file'];

Get the file who start the calling