Question

I just spent hours trying to debug an out of memory error caused by the following code:

for ($i = 1; i <= 4; $i++) {
  $allowed[] = $type.'_'.$i;
}

Which PHP kindly mangles into:

for ($i = 1; 'i' <= 4; $i++) {
  $allowed[] = $type.'_'.$i;
}

This causes an endless loop, which eventually leads to an out of memory error due to appending to the array. PHP will generate a notice level error, and I could change my error reporting level to show these but I am working on a third party application which has a tendency to generate enough of these that this isn’t really a viable solution.

Is there any way to trap these really simple bugs? Ironically, if you do something like constant('i') and explicitly ask for the value it will generate a warning rather than a notice, and this behaviour would be ideal.

Answer 1

You could create a custom error function then filter out the most common errors and only report the less common ones. Then up the error reporting level in PHP. E.g.

function customError($error_no, $error_message, $error_file, $error_line, $error_context) {
    $common_errors = Array('File not found', 'Another made up error', 'Its late');
    if (! in_array($error_message, $common_errors)) {
        // throw exception, log to file, or other action
    }
}

set_error_handler("customError");

You could also filter errors like so:

• Filter out all errors unless they are
  in a file of interest by testing
  $error_file against an array of
  files you maintain

• Even better (not on a production
  server) fetch the last_modified
  date/time of $error_file with
  filemtime() and report the error if
  it was changed within the last 10
  minutes. This helps you debug code as
  you write it

• Or if it’s within a framework which
  yours sounds like it is, break apart
  the path of $error_file and test if
  it’s in your module/view/controller
  files, as opposed to core framework
  files