A Simple Debug Function for PHP

As FileMaker developers, we rely heavily on FileMaker Pro Advanced, which lets us step through scripts and test variables on the fly. Unlike in FileMaker, there is no Data Viewer and Script Debugger to make life easy in PHP development. We can take a manual approach or just as with FileMaker solutions write a custom function to do all the heavy lifting.

The Old Way

When trying to decide the content of variables that fail, developers usually print these to the web browser, using either “echo” for strings or “print_r” for arrays.

We quickly discover that large arrays look messy with just print_r, and so the next step is to wrap some “pre” lines around this to format the array into more readable text.

echo '<pre>';
print_r( $array_name );
echo '</pre>';

Even these three lines can get end up crowding your page as you are writing code. When stepping through the various arrays returned by the PHP API for FileMaker using a newFindCommand, adding these three lines in between each variable, and then commenting these out while debugging, can become tedious. The simple query below has five possible places you might want to check the content of the variable.

$find = $fm->newFindCommand($layout);
$find->addFindCriterion('field', $value);
$result = $find->execute();
if(FileMaker::isError($result)) {
 $error = $result->getMessage();
 die($error);
}
$records = $result->getRecords();
$record = $records[0];

A Better Way

Writing a function for PHP is somewhat similar to the method in FileMaker. The function requires a name, parameters, and calculations to serve the purpose of the function. You can store your functions in a separate functions.php page that you include in your PHP page, and call the function as needed. The function that I created to check what happens to each variable takes an optional parameter in the end to decide whether to output to the browser. So, I can include this function as one line in multiple places without worrying about commenting out the code.

function display_debug($key, $value, $debug=false) {
  if($debug){
    echo ''.$key . " = ";
    switch (gettype($value)) {
      case 'string' :
        echo $value;
        break;
      case 'array' :
      case 'object' :
      default :
        echo '';
        print_r($value);
        echo ''; 
        break;
} } }

There’s nothing too fancy here. I have in fact borrowed the main part of a function that comes with the PHP Site Assistant installed by FileMaker Server. It checks whether the variable is a string or array. I modified the function to include the key or variable name in bold, and also added the “pre” around the print_r to format the array.

Using the Debug Function

When I need to call this function, I simply call one line. The default has only two parameters.

display_debug('$findall',$findall);

Without the optional third parameter, nothing appears on the page. Add a “1” and this function becomes live.

display_debug('$findall',$findall, 1);

The variable inside quotes will let this appear as text, letting you search if multiple variables appear on the page. Often you need stop points after certain sections of code, in which adding the command “die();” would let you focus on just that section.

Debugging code is part and parcel of any development effort. Even when everything seems to work great, to echo the arrays or strings stored in variables validates your code and acts as a sanity check. Testing for errors or determining the cause of errors require stepping through all possible locations this may happen. With a function handling displaying the variable contents and not using print_r() on each page, your code ends up cleaner on each page and cleaner overall.