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Debugging

Debugging is an inevitable and necessary part of any development cycle. While CakePHP doesn’t offer any tools that directly connect with any IDE or editor, CakePHP does provide several tools to assist in debugging and exposing what is running under the hood of your application.

Basic Debugging

debug(mixed $var, boolean $showHtml = null, $showFrom = true)
Parameters:
  • $var (mixed) – The contents to print out. Arrays and objects work well.
  • $showHTML (boolean) – Set to true, to enable escaping. Escaping is enabled by default in 2.0 when serving web requests.
  • $showFrom (boolean) – Show the line and file the debug() occurred on.

The debug() function is a globally available function that works similarly to the PHP function print_r(). The debug() function allows you to show the contents of a variable in a number of different ways. First, if you’d like data to be shown in an HTML-friendly way, set the second parameter to true. The function also prints out the line and file it is originating from by default.

Output from this function is only shown if the core debug variable has been set to a value greater than 0.

Changed in version 2.1: The output of debug() more resembles var_dump(), and uses Debugger internally.

Debugger Class

The debugger class was introduced with CakePHP 1.2 and offers even more options for obtaining debugging information. It has several functions which are invoked statically, and provide dumping, logging, and error handling functions.

The Debugger Class overrides PHP’s default error handling, replacing it with far more useful error reports. The Debugger’s error handling is used by default in CakePHP. As with all debugging functions, Configure::debug must be set to a value higher than 0.

When an error is raised, Debugger both outputs information to the page and makes an entry in the error.log file. The error report that is generated has both a stack trace and a code excerpt from where the error was raised. Click on the “Error” link type to reveal the stack trace, and on the “Code” link to reveal the error-causing lines.

Using the Debugger Class

class Debugger

To use the debugger, first ensure that Configure::read(‘debug’) is set to a value greater than 0.

static Debugger::dump($var, $depth = 3)

Dump prints out the contents of a variable. It will print out all properties and methods (if any) of the supplied variable:

$foo = array(1,2,3);

Debugger::dump($foo);

// outputs
array(
    1,
    2,
    3
)

// simple object
$car = new Car();

Debugger::dump($car);

// outputs
Car
Car::colour = 'red'
Car::make = 'Toyota'
Car::model = 'Camry'
Car::mileage = '15000'
Car::accelerate()
Car::decelerate()
Car::stop()

Changed in version 2.1: In 2.1 forward the output was updated for readability. See Debugger::exportVar()

Changed in version 2.5.0: The depth parameter was added.

static Debugger::log($var, $level = 7, $depth = 3)

Creates a detailed stack trace log at the time of invocation. The log() method prints out data similar to that done by Debugger::dump(), but to the debug.log instead of the output buffer. Note your app/tmp directory (and its contents) must be writable by the web server for log() to work correctly.

Changed in version 2.5.0: The depth parameter was added.

static Debugger::trace($options)

Returns the current stack trace. Each line of the trace includes the calling method, including which file and line the call originated from.

//In PostsController::index()
pr(Debugger::trace());

//outputs
PostsController::index() - APP/Controller/DownloadsController.php, line 48
Dispatcher::_invoke() - CORE/lib/Cake/Routing/Dispatcher.php, line 265
Dispatcher::dispatch() - CORE/lib/Cake/Routing/Dispatcher.php, line 237
[main] - APP/webroot/index.php, line 84

Above is the stack trace generated by calling Debugger::trace() in a controller action. Reading the stack trace bottom to top shows the order of currently running functions (stack frames). In the above example, index.php called Dispatcher::dispatch(), which in-turn called Dispatcher::_invoke(). The _invoke() method then called PostsController::index(). This information is useful when working with recursive operations or deep stacks, as it identifies which functions are currently running at the time of the trace().

static Debugger::excerpt($file, $line, $context)

Grab an excerpt from the file at $path (which is an absolute filepath), highlights line number $line with $context number of lines around it.

pr(Debugger::excerpt(ROOT . DS . LIBS . 'debugger.php', 321, 2));

//will output the following.
Array
(
    [0] => <code><span style="color: #000000"> * @access public</span></code>
    [1] => <code><span style="color: #000000"> */</span></code>
    [2] => <code><span style="color: #000000">    function excerpt($file, $line, $context = 2) {</span></code>

    [3] => <span class="code-highlight"><code><span style="color: #000000">        $data = $lines = array();</span></code></span>
    [4] => <code><span style="color: #000000">        $data = @explode("\n", file_get_contents($file));</span></code>
)

Although this method is used internally, it can be handy if you’re creating your own error messages or log entries for custom situations.

static Debugger::exportVar($var, $recursion = 0)

Converts a variable of any type to a string for use in debug output. This method is also used by most of Debugger for internal variable conversions, and can be used in your own Debuggers as well.

Changed in version 2.1: This function generates different output in 2.1 forward.

static Debugger::invoke($debugger)

Replace the CakePHP Debugger with a new instance.

static Debugger::getType($var)

Get the type of a variable. Objects will return their class name

New in version 2.1.

Using Logging to debug

Logging messages is another good way to debug applications, and you can use CakeLog to do logging in your application. All objects that extend Object have an instance method log() which can be used to log messages:

$this->log('Got here', 'debug');

The above would write Got here into the debug log. You can use log entries to help debug methods that involve redirects or complicated loops. You can also use CakeLog::write() to write log messages. This method can be called statically anywhere in your application anywhere CakeLog has been loaded:

// In app/Config/bootstrap.php
App::uses('CakeLog', 'Log');

// Anywhere in your application
CakeLog::write('debug', 'Got here');

Debug Kit

DebugKit is a plugin that provides a number of good debugging tools. It primarily provides a toolbar in the rendered HTML, that provides a plethora of information about your application and the current request. You can download DebugKit from GitHub.

xdebug

If your environment supplies the xdebug php extension, fatal errors will show additional xdebug stack trace details. Details about xdebug .