Go4Expert - Debugging PHP Scripts

Smart Debugger of PHP Scripts

Today nobody really questions benefits of using source level debuggers for any language including PHP - debugger is simply a tool, necessity in everyday programmers work. However, it is interesting to note that code validating tools are much less known and it is those tools that are very valuable addition to debuggers in code development.

Traditionally, in compiled languages, certain part of code validation (type checking, checking for non-initialized variables) are usually taken by compiler, but besides compiler there are also external tools used to conduct this task (for example checkstyle for Java). This article deals with use of those tools during development of PHP applications (we will be using Codenizer).

Basic question that programmer asks herself/himself when introducing one new tool into development process is "What benefit can I expect from using this?". Answer to this question is very simple - it is dramatic time saver during development, and we all know what that means in today's world of merciless business competition - more time you save in development of one application faster you can switch to next application, which means more money for you.

Code verification/checking tools are complementary to debuggers - usual way of using debugger is after encountering program malfunction to better analyze reasons that led to unexpected behavior and in the end to eliminate those reasons (i.e. bugs). On the other hand, code verification tools are used during program development to pinpoint possible problematic locations which could eventually lead to bugs in program - so debuggers are used to eliminate bugs once they are in program, code validation tools are used to prevent bugs from appearing in the program in the first place.

Simple example

To better illustrate basic operation of validating tools let's consider this simple PHP script (schedule.php, given with line numbers to be easier to follow):

PHP Code:


		
			
01 <?php

02

03 class Schedule {

04    private $SID;

05    private $SDate;

06    private $flights;

07

08    // Set methods

09    function set_SID($SID) {

10        $this->SID = $SID;

11    }

12    function set_SDate($SDate) {

13        $this->SDate = $SDate;

14    }

15    function set_flights($flights) {

16        $this->flights = $flights;

17    }

18

19    // Get methods

20    function get_SID() {

21        return $this->SID;

22    }

23    function get_SDate() {

24        return $this->SDate;

25    }

26    function get_flights() {

27        return $this->fligths;

28    }

29    function __construct($sid, $sdate, $flights) {

30        $this->SID = $sid;

31        $this->SDate = $sdate;

32        $flights = split(';', $flights);

33        $this->flights = array();

34        for ($i = 0; $i < count($flight); $i++)

35            $this->flights[] = $i . '. ' . $flight[$i];

36    }

37 }

38 ?>

After invoking code validation tool (bellow is example screen shot how it looks within Eclipse), we are presented with tool's report:

http://www.go4expert.com/images/arti...er-eclipse.png

As we can see in the report are mentioned 3 potentially problematic spots which should be closer inspected by programmer:

'Performance - function called in condition part of loop' on line 34 - calling function in condition checking part of loop usually impose certain performance penalty (since PHP interpreter usually doesn't optimize it), but it can be avoided by using auxiliary variable - for example $cnt = count($flight);
for ($i = 0; $i < $cnt; $i++)...
'Undeclared property 'fligths' in class 'Schedule'' on line 27 - this is obviously typo, should be $this->flights;
'Uninitialized variable 'flight'' on line 34 - another typo, should be count($flights).

We can see that it only took less than a second to detect 2 bugs and 1 performance tip, all without leaving the development environment or starting program. Compared to classical debugging this is real time saver, not to say how difficult could be to trace those errors with debugger especially if class Schedule was part of bigger project. This is however just small fraction of checks that code validation tools usually perform.

Where to Start

First of all you need tool itself (like Codenizer), then some IDE that supports PHP development (Eclipse or NetBeans would be smart choice), and plugin for integrating tool with IDE which can be found in the same location as tool.

Conclusion

It would be wrong to think of code validation as of some magic that would forever relieve you of using debugger and make you make bug-free code. Code validation can't do that for you, but what it can do is to reduce your time spent debugging program by almost 80% and it can help you spot the problems that could otherwise go unseen for very long time.