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HTML Multi checkbox set – the correct way to group checkboxes

February 15th, 2012

I was setting up an HTML form today and I wanted to group some options together in a multi checkbox set, allowing a user to select multiple options in a category. I usually just give each checkbox a unique name and parse all of the individual values in PHP, but this has always struck me as an ugly way to handle this use case.

As I was looking up the syntax for an HTML checkbox, I found a lot of info that said I could simply name all of the checkboxes the same and it would group all of the values together like this:

<input type="checkbox" name="chk_group" value="value1" />Value 1<br />
<input type="checkbox" name="chk_group" value="value2" />Value 2<br />
<input type="checkbox" name="chk_group" value="value3" />Value 3<br />

But this doesn’t work. When you POST the values to PHP, you only receive the last item selected in the group. The annoying thing is that a lot of the examples online show this same syntax even though it’s clearly wrong. After digging a little deeper, I found this forum post with the correct syntax. Adding square braces to the checkbox name creates an array of the selected values in the group:

<input type="checkbox" name="chk_group[]" value="value1" />Value 1<br />
<input type="checkbox" name="chk_group[]" value="value2" />Value 2<br />
<input type="checkbox" name="chk_group[]" value="value3" />Value 3<br />

This can be retrieved in PHP with a simple loop:

<?php
if (isset($_POST['chk_group'])) {
    $optionArray = $_POST['chk_group'];
    for ($i=0; $i<count($optionArray); $i++) {
        echo $optionArray[$i]."<br />";
    }
}
?>

Simple! I thought I should post this correct solution in the hopes that it might help someone else wade through all of the wrong information out there.

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