PHP Forms Validating Form Input: Radio Buttons

PHP Forms 

Validating Form Input: Radio Buttons

Problem

You want to make sure a valid radio button is selected from a group of radio buttons.

Solution

Use an array of values to generate the menu. Then validate the input by checking that the submitted value is in the array.

Example  Validating a radio button

          // Generating the radio buttons

          $choices = array('eggs' => 'Eggs Benedict',

                                          'toast' => 'Buttered Toast with Jam',

                                          'coffee' => 'Piping Hot Coffee');

          foreach ($choices as $key => $choice) {

                echo "<input type='radio' name='food' value='$key'/> $choice \n";

          }

          // Then, later, validating the radio button submission

          if (! array_key_exists($_POST['food'], $choices)) {

                echo "You must select a valid choice.";

          }

Discussion

The radio button validation is very similar to the drop-down menu validation. They both follow the same pattern—define the data that describes the choices, generate the appropriate HTML, and then use the defined data to ensure that a valid value was submitted. The difference is in what HTML is generated.

One difference between drop-down menus and radio buttons is how defaults are handled. When the HTML doesn’t explicitly specify a default choice for a drop-down menu, the first choice in the menu is used. However, when the HTML doesn’t explicitly specify a default choice for a set of radio buttons, no choice is used as a default.

To ensure that one of a set of radio buttons is chosen in a well-behaved web browser, give the default choice a checked="checked" attribute. In the following code, toast is the default:

          // Defaults

          $defaults['food'] = 'toast';

          // Generating the radio buttons

          $choices = array('eggs' => 'Eggs Benedict',

                                          'toast' => 'Buttered Toast with Jam',

                                          'coffee' => 'Piping Hot Coffee');

          foreach ($choices as $key => $choice) {

                echo "<input type='radio' name='food' value='$key'";

                if ($key == $defaults['food']) {

                      echo ' checked="checked"';

                }

                echo "/> $choice \n";

          }

          // Then, later, validating the radio button submission

          if (! array_key_exists($_POST['food'], $choices)) {

                echo "You must select a valid choice.";

          }

In addition, to guard against missing values in hand-crafted malicious requests, use filter_has_var() to ensure that something was submitted for the radio button.