(PHP 5, PHP 7)
debug_print_backtrace — Prints a backtrace
$options = 0
[, int $limit = 0
]] )debug_print_backtrace() prints a PHP backtrace. It prints the function calls, included/required files and eval()ed stuff.
optionsAs of 5.3.6, this parameter is a bitmask for the following options:
| DEBUG_BACKTRACE_IGNORE_ARGS | Whether or not to omit the "args" index, and thus all the function/method arguments, to save memory. |
limit
As of 5.4.0, this parameter can be used to limit the number of stack frames printed.
By default (limit=0) it prints all stack frames.
No value is returned.
| Version | Description |
|---|---|
| 5.4.0 |
Added the optional parameter limit.
|
| 5.3.6 |
Added the optional parameter options.
|
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]
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()));
?>
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 $trace;
}
?>
This functionality is now implemented in the PEAR package PHP_Compat.
More information about using this function without upgrading your version of PHP can be found on the below link:
http://pear.php.net/package/PHP_Compat
This code will give you a simple horizontal stack trace to assist debugging:
<?php
class A {
public function testA() {
echo "<LI>Class A.testA ----??";
echo "<LI>".$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
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).')';
}
}
?>
If you want to get the trace into a variable or DB, I suggest to do the following:
<?php
ob_start();
debug_print_backtrace();
$trace = ob_get_contents();
ob_end_clean();
$query = sprintf("INSERT INTO EventLog (Trace) VALUES ('%s')",
mysql_real_escape_string($trace));
mysql_query($query);
?>
bortuzar: a simpler version, w/o output buffering:
<?php
$query = sprintf("INSERT INTO EventLog (Trace) VALUES ('%s')",
mysql_real_escape_string(join("\n", debug_backtrace())) );
mysql_query($query);
?>
