Creating simple debug-tool with php

Jussi Pohjolainen

Tampere University of Applied Sciences » Computer Science

Intro to debug

• When program is syntactically correct but logically flawed, debugging comes to rescue.
• Debug: tracing code variables, output etc.
• There are many premade tools for php debugging (Eclipse PHP IDE, Zend Studio)
• It's not very hard to create a simple debugging tools by yourself.

Creating simple debug-tool

• Every method and function has input and output values.
• For tracing these values you could simply print them:

  function myFunction ($input)
  {
      print "Input: [$input]";
      // Some logic here
      $ret = $input*2;
      print "Return: [$ret]";
      return $ret;
  }
  

• Problem with this is that the function prints always debugging information.

Setting global debug-variable

• One way of dealing debug-information is to set a $DEBUG - variable to the application's configuration file.
• For example, file conf.php could hold variable called $DEBUG and it's value could be set to true or false.
• If $DEBUG is set to true, debug-information is printed.

Example

require_once("conf/conf.php");
function myFunction ($input)
{
    global $DEBUG;
    if($DEBUG)
    {
        print "Input: [$input]";
    }
    // Some logic here
    $ret = $input*2;
    if($DEBUG)
    {
        print "Return: [$ret]";
    }
    return $ret;
}

Setting ID

• Debug-information might be confusing this way ("What's the function that prints this debug information?")
• The output could be like "Class.function", for example: Math.min: Input [8,7]
• See example: myfunction.php

Creating debug-function

• It would be wise to create debug-function that prints the debug information
• This way it's easy to make changes to debug printing code
• See example: myfunction2.php

Debug Levels

• $DEBUG is now set to TRUE or FALSE. => debug is either on or off.
• It would be a better if there were detail-levels of debug.
• So instead of using true or false, we could use integer 1-10.
• Level 1: Input and output of the function
• Level 2: One brace deeper: input and output
• Level 3: One brace deeper: input and output
• Level 4: ..
• See example: myfunction3.php

Creating Debug-class

class Debug
{
    private $className;
    public function __construct ( $className )
    {
        $this->className = $className;
    }
    public function debug ($functionName, $message, $level = 1) { ... }
}

class Math extends Debug
{
    public function __construct ()   // PHP5
    {
        parent::__construct("Math");
    }
}