[Obsolete] Write E_ALL compliant code

Adjusting the error reporting level

Drupal 6.x releases ignore E_NOTICE, E_STRICT, and E_DEPRECATED notices for the benefit of production sites. To view all PHP errors on development or testing sites, you may change includes/common.inc from:

  if ($errno & (E_ALL ^ E_DEPRECATED ^ E_NOTICE)) {

to:

  if ($errno & (E_ALL | E_STRICT)) {

Drupal 7.x releases report any error levels which are part of E_ALL, and allow PHP to be configured to report additional error levels, such as E_STRICT. To view all PHP errors on development or testing sites, you may set

php_value error_reporting -1

in the .htaccess file.

Use of isset() or !empty()

If you want to test the value of a variable, array element or object property, you may need to use if (isset($var)) or if (!empty($var)) rather than if ($var) if there is a possibility that $var has not been defined.

The difference between isset() and !empty() is that unlike !empty(), isset() will return TRUE even if the variable is set to an empty string or zero. In order to decide which one to use, consider whether '' or 0 are valid and expected values for your variable.

The following code may trigger an E_NOTICE error:

function _form_builder($form, $parents = array(), $multiple = FALSE) {
  // (...)
  if ($form['#input']) {
    // some code (...)
  }
}

Here, the variable $form is passed on to the function. If $form['#input'] evaluates as true, some code is executed. However, if $form['#input'] does not exist, the function outputs the following error message: notice: Undefined index: #input in includes/form.inc on line 194.

Even though the array $form is already declared and passed to the function, each array index must be explicitly declared. The previous code should read:

function _form_builder($form, $parents = array(), $multiple = FALSE) {
  // (...)
  if (!empty($form['#input'])) {
    // some code (...)
  }
}

Beware!

The function isset() returns TRUE when the variable is set to 0, but FALSE if the variable is set to NULL. In some cases, is_null() is a better choice, especially when testing the value of a variable returned by an SQL query.