isset($_POST['x']) only works if the submit button name="submit"

Question

I'm having trouble using postback because I've more than one form and isset only works with name="submit" buttons.

My code will work fine if I use name="submit" but if I changed the name to something else, isset($_POST['somethingelse']) will always be false, why does this happen?

EDIT:

<input type="submit" name="submit" value="Submit" onclick ="validate(document.getElementById('form')); return false;" />

if (isset($_POST['submit'])) <-- works as expected



<input type="submit" name="asdf" value="Submit" onclick ="validate(document.getElementById('form')); return false;" />


if (isset($_POST['asdf'])) <-- does not works as expected

---

EDIT2:

<?php
$validated = false;
if (isset($_POST['submit'])) {
    // preserve form values by storing the values from $_POST into variables
    $test = $_POST['test'];
    // validated is now true as submit button only submits if validated (script)
    $validated = true;
} else {
    // make variables empty as there's no values to preserve
        $test = '';
}

if (!$validated) {
?>
<form id="form" action="<?php echo $_SERVER['PHP_SELF'] ?>" method="post">
<p>Test: <input type="text" name="test" size="20" value="<?php echo $test ?>" /></p>
<p><input type="submit" name="submit" value="Submit" onclick ="validate(); return false;" /></p>
<?php } ?>

For example here, works as expected (I can keep the values) as name="submit" and if (isset($_POST['submit'])) is true when the button submits but if I change both the name="" and the if (isset($_POST[''])) then it will not work as the isset is returning false (even though the button submits).

Answer 1

It's normal because only the clicked submit button is set and not the second, if you click on submit button with name submit isset($_POST['submit']) will give you true and isset($_POST['asdf']) false, and if you click on asdf isset($_POST['submit']) gives false and isset($_POST['asdf']) true, i tested it and it works without any problem.

Test code:

<?php
$validated = false;
if (isset($_POST['submit'])) {
    // preserve form values by storing the values from $_POST into variables
    $test = "submit";
    // validated is now true as submit button only submits if validated (script)
    $validated = true;
} 
else if(isset($_POST['asdf'])){
        $test = "asdf";
    // validated is now true as submit button only submits if validated (script)
    $validated = true;
}
else {
    // make variables empty as there's no values to preserve
        $test = '';
}
if (!$validated) {
echo $test;
} ?>
<form id="form" action="<?php echo $_SERVER['PHP_SELF'] ?>" method="post">
<p>Test: <input type="text" name="test" size="20" value="<?php echo $test ?>" /></p>
<p><input type="submit" name="submit" value="Submit" onclick ="validate(); return false;" /></p>
<p><input type="submit" name="asdf" value="Submit" onclick ="validate(document.getElementById('form')); return false;" />
</p>