How to recover unchecked checkbox values with PHP

Question

I need to identify checkbox fields that are unchecked via PHP

Answer 1

simple, assemble a ternary:

$checboxName = isset($_POST['name'])?true:false;

if it exists then it was set, if not.

EDIT

In case you have many checkboxs and do not wish to check them all via ternary, you must make a event in javascript to set in value in the input before it is sent.

<?php
echo '<pre>';
var_dump($_POST);
echo '</pre>';
?>

<form method="post" id="form">
    <input type="checkbox" name="name">
    <input type="submit" value="send">
</form>

<script type="text/javascript">
    document.getElementById('form').addEventListener('submit', function(){ // CRIA EM EVENTO QUE É DISPARADO QUANDO O ELEMENTO DE ID 'form' FOR 'submetido/enviado'.
        var inputs = this.getElementsByTagName('input'); // PEGA TODOS OS INPUTS PRESENTES NESSE ELEMENTO
        for(var i in inputs){ // ITERA OS INPUTS
            var input = inputs[i];
            if(input.type == 'checkbox'){ // CASO SEJA UM 'checkbox'
                input.value = input.checked; // SETA 'value' COM TRUE/FALSE DE ACORDO COM O CHECKED
            }
            input.checked = true; // SETA COMO CHECKED PARA QUE ELE SEJA ENVIADO, O VALOR VALIDO É O QUE ESTA NO 'value' DO ELEMENTO
        }
    });
</script>

Problems

• This method generates a bad visual effect, because when submitting the form all checked are marked, even if they are not true, to solve this you can use ajax.
• PHP captures the value of $_POST as string. Then even sent true/false, this sera string. To solve this problem you can use this function.

Checks String true/false

function is_true($var){
    if(is_string($var)){
        if(preg_match('~^(false|f)$~', $var) != null){
            return false;
        }
    }
    return !!$var;
}