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debug_print_backtrace

(PHP 5, PHP 7, PHP 8)

debug_print_backtrace Prints a backtrace

Description

debug_print_backtrace(int $options = 0, int $limit = 0): void

debug_print_backtrace() prints a PHP backtrace. It prints the function calls, included/required files and eval()ed stuff.

Parameters

options

This parameter is a bitmask for the following options:

debug_print_backtrace() options
DEBUG_BACKTRACE_IGNORE_ARGS Whether or not to omit the "args" index, and thus all the function/method arguments, to save memory.

limit

This parameter can be used to limit the number of stack frames printed. By default (limit=0) it prints all stack frames.

Return Values

No value is returned.

Examples

Example #1 debug_print_backtrace() example

<?php
// include.php file

function a() {
    
b();
}

function 
b() {
    
c();
}

function 
c(){
    
debug_print_backtrace();
}

a();

?>
<?php
// test.php file
// this is the file you should run

include 'include.php';
?>

The above example will output something similar to:

#0  c() called at [/tmp/include.php:10]
#1  b() called at [/tmp/include.php:6]
#2  a() called at [/tmp/include.php:17]
#3  include(/tmp/include.php) called at [/tmp/test.php:3]

See Also

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User Contributed Notes 5 notes

up
60
bishop
12 years ago
Another way to manipulate and print a backtrace, without using output buffering:

<?php
// print backtrace, getting rid of repeated absolute path on each file
$e = new Exception();
print_r(str_replace('/path/to/code/', '', $e->getTraceAsString()));
?>
up
22
dany dot dylan at gmail dot com
12 years ago
I like the output of debug_print_backtrace() but I sometimes want it as a string.

bortuzar's solution to use output buffering is great, but I'd like to factorize that into a function.  Doing that however always results in whatever function name I use appearing at the top of the stack which is redundant.

Below is my noddy (simple) solution.  If you don't care for renumbering the call stack, omit the second preg_replace().

<?php
   
function debug_string_backtrace() {
       
ob_start();
       
debug_print_backtrace();
       
$trace = ob_get_contents();
       
ob_end_clean();

       
// Remove first item from backtrace as it's this function which
        // is redundant.
       
$trace = preg_replace ('/^#0\s+' . __FUNCTION__ . "[^\n]*\n/", '', $trace, 1);

       
// Renumber backtrace items.
       
$trace = preg_replace ('/^#(\d+)/me', '\'#\' . ($1 - 1)', $trace);

        return
$trace;
    }
?>
up
-2
David Spector
11 months ago
If your show your error messages in HTML (with suitable safety using entities), this function won't work nicely because it uses newlines for formatting.

Here is a function that works similarly, but using <BR> tags. Insert it near the beginning of your program to add a stack to Warning output only, or modify it as you like:

// Here is code for error stack output in HTML:
function error_handler_callback($errno,$message,$file,$line,$context)
    {
    if ($errno === E_WARNING)
        echo "Stack, innermost first:<br>".nl2br((new Exception())->getTraceAsString());
    return false; // to execute the regular error handler
    }
set_error_handler("error_handler_callback");
up
-10
AB
5 years ago
This code will give you a simple horizontal stack trace to assist debugging:

<?php

class A {
    public function
testA() {
        echo
"<LI>Class A.testA ----??";
        echo
"<LI>".$this->whoDidThat();
    }
    public function
whoDidThat() {
       
$who=debug_backtrace();
       
$result="";
       
$count = 0;
       
$last=count($who);
        foreach(
$who as $k=>$v) {
            if (
$count++ > 0) {
               
$x="";
                if (
$count>2) {
                   
$x=">";
                }
               
$result="[line".$who[$k]['line']."]".$who[$k]['class'].".".$who[$k]['function'].$x.$result;
            }
        }
        return
$result;
    }
}
class
B extends A {
    public function
testB() {
        echo
"<LI>Class B.testB";
        echo
"<LI>".$this->whoDidThat();
    }
    public function
testA() {
        echo
"<LI>Class testB.testA  ---- Y";
        echo
"<LI>".$this->whoDidThat();
    }
}
class
C {
    public function
test() {
        echo
"<HR>";
       
$b=new B();
        echo
"<HR>Class C calling B.testA";
       
$b->testA();
    }
}

$c=new C();
$c->test();
echo
debug_print_backtrace();
?>

When run you get

Class C calling B.testA
*Class testB.testA ---- Y
*[line45]C.test>[line40]B.testA
up
-12
chris dot kistner at gmail dot com
11 years ago
Here's a function that returns a string with the same information shown in debug_print_backtrace(), with the option to exclude a certain amount of traces (by altering the $traces_to_ignore argument).

I've done a couple of tests to ensure that it prints exactly the same information, but I might have missed something.

This solution is a nice workaround to get the debug_print_backtrace() information if you're already using ob_start() in your PHP code.

<?php
function get_debug_print_backtrace($traces_to_ignore = 1){
   
$traces = debug_backtrace();
   
$ret = array();
    foreach(
$traces as $i => $call){
        if (
$i < $traces_to_ignore ) {
            continue;
        }

       
$object = '';
        if (isset(
$call['class'])) {
           
$object = $call['class'].$call['type'];
            if (
is_array($call['args'])) {
                foreach (
$call['args'] as &$arg) {
                   
get_arg($arg);
                }
            }
        }       

       
$ret[] = '#'.str_pad($i - $traces_to_ignore, 3, ' ')
        .
$object.$call['function'].'('.implode(', ', $call['args'])
        .
') called at ['.$call['file'].':'.$call['line'].']';
    }

    return
implode("\n",$ret);
}

function
get_arg(&$arg) {
    if (
is_object($arg)) {
       
$arr = (array)$arg;
       
$args = array();
        foreach(
$arr as $key => $value) {
            if (
strpos($key, chr(0)) !== false) {
               
$key = '';    // Private variable found
           
}
           
$args[] =  '['.$key.'] => '.get_arg($value);
        }

       
$arg = get_class($arg) . ' Object ('.implode(',', $args).')';
    }
}
?>
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