How to debug code in PHP?

Question

For example, in javascript we have the console.log to debug, find out where the bugs are, etc. And in PHP, which ones would be best manners?

Answer 1

Consider using the function debug_backtrace PHP, but only in development, because the function has a great computational cost.

Documentation: http://php.net/debug_backtrace

---

Use like this:

$is_dev = true;

function debug() {
    global $is_dev;

    if ($is_dev) {
        $debug_arr = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
        $line = $debug_arr[0]['line'];
        $file = $debug_arr[0]['file'];

        header('Content-Type: text/plain');

        echo "linha: $line\n";
        echo "arquivo: $file\n\n";
        print_r(array('GET' => $_GET, 'POST' => $_POST, 'SERVER' => $_SERVER));
        exit;
    }
}

// ...

if (/* ... */) {
    debug();

    /*
    Nesse ponto, a execução do script será interrompida
    e serão impressos o nº da linha atual, o nome do arquivo e as variáveis
    $_GET, $_POST e $_SERVER
    */
}

Making some adaptations to your case, the function looks great to debug the code!

See also:

• var_dump - http://br2.php.net/manual/en/function.var-dump.php
• print_r - http://br2.php.net/manual/en/function.print-r.php
• var_export - http://br1.php.net/var_export
• debug_print_backtrace - http://br1.php.net/debug_print_backtrace
• __LINE__ and __FILE__ - http://br1.php.net/manual/en/language.constants.predefined.php

Answer 2

In PHP, the direct equivalent of console.log would be print_r, var_dump and the var_export.

If you have the xdebug enabled, can also use the xdebug_var_dump which displays the output mode also pre-formatted and colored.

Now, what about the best debugging mode? Well, it depends on each case. It can be by printing the screens as I said, or with an integrated IDE with xdebug or pre-defined equivalent and may even set breakpoints.

Short summary with main differences

• print_r : simpler. Does not export with types
• var_dump: more detailed. Exports types. Useful in cases where it has values 0, ', NULL.
• var_export: similar to var_dump, but exports a code that can be reused again in your Script.

Advanced

It is also possible to debug an application during code execution. For this you will need an IDE and some module that, when your script runs, allows any tool that connects to a specific port to interact with your script.

Answer step by step this is reason for another exclusive question, but a reference to know more about it can be seen in Debugging PHP Source Code in Netbeans IDE

Although it is the most advanced medium, it can be complex to configure and more time consuming than testing with print_r and die. But it is excellent in more complex applications.

Answer 3

In php we have the var_dump() which returns the element to be debugged and all its properties.

Mentioning the php documentation the var_dump() Dve be used like this:

Examples

Example #1 Example from var_dump()

<?php
$a = array (1, 2, array ("a", "b", "c"));
var_dump ($a);
?>

The above example will print:

/* mostrará:
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  array(3) {
    [0]=>
    string(1) "a"
    [1]=>
    string(1) "b"
    [2]=>
    string(1) "c"
  }
}

Example #2 Example from var_dump()

<?php

$b = 3.1;
$c = true;
var_dump($b,$c);

?>

The above example will print:

float(3.1)
bool(true)

Answer 4

The most practical option to debug in PHP is to install a debbuger as Xdebug or Zend Debugger in conjunction with an IDE (Eclipse, Netbeans, Phpstorm etc) this combination allows:

• That PHP code be paused at any time with a breakpoint.

• Inspection of variables and their values.

• It is possible to profile performance, which helps to efficiently detect bottlenecks or slowness.

Installation Xdebug

Go to http://xdebug.org/ download the specific version of your php and throw the file in the extensions folder (usually ext).

Setup

Open php.ini and add the following lines and restart apache to put the changes into effect.

[XDebug]
zend_extension = "php_xdebug.dll"
xdebug.remote_handler = "dbgp"
xdebug.remote_host = "localhost"
xdebug.remote_port=9000
xdebug.remote_enable = On

Thus the Xdebug will be activated via demand, ie it is necessary to inform the query string XDEBUG_SESSION_START on all pages you want to enable it. To facilitate the process there are extensions for Firefox (Xdebug cute) and Chrome (Xdebug helper) who do this job.

If you want to enable debug on all requests made add this line:

xdebug.remote_autostart=On

Answer 5

You can use a lib called dephpugger. It’s like ipdb for python or byebug for ruby. You type xdebug_break() in your code and it stops at the terminal.

https://github.com/tacnoman/dephpugger

Answer 6

I don’t know where you are developing, but if it were on a Linux system it would be nice for you to disable errors by php.ini changing the keys expose_php = off and display_erros = off. So your system would be safer and could view kernel errors.

By Ubuntu you would use the following command:

$: tail -f /var/log/apache2/error.log

Answer 7

Place this line at the point you want to debug:

echo "TRACE at:".__FILE__.":".__LINE__.":<br\><pre>". debug_string_backtrace()."</pre>"; exit;

Answer 8

A strategy that works in almost every environment is writing a log file:

<?php
$test = 'My variable value';
file_put_contents('./my-log.txt', 'test='.$test);

Answer 9

If you want to know the value of a variable, you can only use:

die(var_dump($variavel));