How to access the form's 'name' variable from PHP

Question

I'm trying to create a BMI calculator. This should allow people to use either metric or imperial measurements.

I realise that I could use hidden tags to solve my problem, but this has bugged me before so I thought I'd ask: I can use $_POST['variableName'] to find the submitted variableName field-value; but...I don't know, or see, how to verify which form was used to submit the variables.

My code's below (though I'm not sure it's strictly relevant to the question):

<?php
    $bmiSubmitted     = $_POST['bmiSubmitted'];

    if (isset($bmiSubmitted)) {
        $height        = $_POST['height'];
        $weight        = $_POST['weight'];
        $bmi        = floor($weight/($height*$height));

        ?>
            <ul id="bmi">
            <li>Weight (in kilograms) is: <span><?php echo "$weight"; ?></span></li>

            <li>Height (in metres) is: <span><?php echo "$height"; ?></span></li>

            <li>Body mass index (BMI) is: <span><?php echo "$bmi"; ?></span></li>

            </ul>
        <?php
    }

    else {
    ?>

    <div id="formSelector">

    <ul>
        <li><a href="#metric">Metric</a></li>
        <li><a href="#imperial">Imperial</a></li>
    </ul>

        <form name="met" id="metric" action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" enctype="form/multipart">

            <fieldset>
                <label for="weight">Weight (<abbr title="Kilograms">kg</abbr>):</label>
                    <input type="text" name="weight" id="weight" />

                <label for="height">Height (<abbr title="metres">m</abbr>):</label>
                    <input type="text" name="height" id="height" />

                <input type="hidden" name="bmiSubmitted" id="bmiSubmitted" value="1" />
            </fieldset>

            <fieldset>
                <input type="reset" id="reset" value="Clear" />

                <input type="submit" id="submit" value="Submit" />
            </fieldset>
        </form>

        <form name="imp" id="imperial" action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" enctype="form/multipart">

            <fieldset>

            <label for="weight">Weight (<abbr title="Pounds">lbs</abbr>):</label>
                <input type="text" name="weight" id="weight" />

            <label for="height">Height (Inches):</label>
                <input type="text" name="height" id="height" /
            <input type="hidden" name="bmiSubmitted" id="bmiSubmitted" value="1" />
            </fieldset>

            <fieldset>
                <input type="reset" id="reset" value="Clear" />
                <input type="submit" id="submit" value="Submit" />
            </fieldset>
        </form>

    <?php
    }
?>

I verified that it worked (though without validation at the moment -I didn't want to crowd my question too much) with metric; I've added the form but not the processing for the imperial yet.

As some have noted below, the form's name shouldn't really be important. If you need to distinguish data from one form or another it's probably better for each form to have a different action. — rojoca
– rojoca, Commented May 10, 2009 at 22:02

Peter Mortensen · Accepted Answer · 2021-09-26 21:09:57Z

96

To identify the submitted form, you can use:

A hidden input field.
The name or value of the submit button.

The name of the form is not sent to the server as part of the POST data.

You can use code as follows:

<form name="myform" method="post" action="" enctype="multipart/form-data">
    <input type="hidden" name="frmname" value=""/>
</form>

edited Sep 26, 2021 at 21:09

Peter Mortensen

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answered May 10, 2009 at 20:13

Ayman Hourieh

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Comments

Peter Mortensen · Accepted Answer · 2021-09-26 21:19:35Z

19

You can do it like this:

<input type="text" name="myform[login]">
<input type="password" name="myform[password]">

Check the posted values

if (isset($_POST['myform'])) {
    $values = $_POST['myform'];

    // $login = $values['login'];
    // ...
}

edited Sep 26, 2021 at 21:19

Peter Mortensen

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answered Feb 19, 2013 at 13:13

Seb

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1 Comment

eklingen Over a year ago

I really like that way of going about it! My only question is, how would that work with input groups like checkboxes or radios? Is name="myform[chkgrp][]" valid?

Paolo Bergantino · Accepted Answer · 2009-05-10 20:12:27Z

13

The form name is not submitted. You should just add a hidden field to each form and call it a day.

answered May 10, 2009 at 20:12

Paolo Bergantino

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4 Comments

David Thomas Over a year ago

Really? That seems like a half-hearted implementation of forms... o.O Still, I feel better for being unable to see how it works.

strager Over a year ago

@ricebowl, A form's name is only useful for DOM manipulations and such.

Narcissus Over a year ago

@ricebowl: understand, too, that this is how HTTP works. It has nothing to do with PHP.

David Thomas Over a year ago

@Strager, I hadn't realised that 'til now. I thought it would have more use, for some reason. @Narcissus, I was intending my criticism, unjust as it may be, to be read as against browsers/http, rather than php.

Peter Mortensen · Accepted Answer · 2016-11-22 22:35:12Z

9

In the form submitting button (id method of form is post):

<input type="submit" value="save" name="commentData">

In the PHP file:

if (isset($_POST['commentData'])){
    // Code
}

edited Nov 22, 2016 at 22:35

Peter Mortensen

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answered May 8, 2012 at 8:48

Ruwantha

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Comments

Peter Mortensen · Accepted Answer · 2021-09-26 21:20:27Z

5

For some reason, the name of the submit button is not passed to the superglobal $_POST when submitted with Ajax/jQuery.

edited Sep 26, 2021 at 21:20

Peter Mortensen

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answered Jan 18, 2014 at 16:09

albator

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1 Comment

Peter Mortensen Over a year ago

That may be true, but how does that answer the question? Can you elaborate? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

Peter Mortensen · Accepted Answer · 2021-09-26 21:25:10Z

Use a unique value on the submit button for each form like so

File index.html

<form method="post" action="bat/email.php">
    <input type="text" name="firstName" placeholder="First name" required>
    <input type="text" name="lastName" placeholder="Last name" required>
    <button name="submit" type="submit" value="contact">Send Message</button>
</form>

<form method="post" action="bat/email.php">
    <input type="text" name="firstName" placeholder="First name" required>
    <input type="text" name="lastName" placeholder="Last name" required>
    <button name="submit" type="submit" value="support">Send Message</button>
</form>

File email.php

<?php
    if (isset($_POST["submit"])) {
        switch ($_POST["submit"]) {
            case "contact":
                break;
            case "support":
                break;
            default:
                break;
        }
    }
?>

Community · Accepted Answer · 2017-05-23 12:18:30Z

2

As petervandijck.com pointed out, this code may be susceptible to XSS attacks if you have it behind some kind of log-in system or have it embedded in other code.

To prevent an XSS attack, where you have written:

<?php echo "$weight"; ?>

You should write instead:

<?php echo htmlentities($weight); ?>

Which could even be better written as:

<?=htmlentities($weight); ?>

edited May 23, 2017 at 12:18

CommunityBot

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answered Sep 8, 2009 at 5:18

Lachlan McDonald

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3 Comments

happy Over a year ago

<? ?> is not supported everywhere. I noticed some shared hosting, even when up-to-date has the option switch off in the php configuration file, even when php version is up-to-date

Peter Mortensen Over a year ago

This should be a comment to the question, not an answer.

Peter Mortensen Over a year ago

The link is broken. Are you referring to PeterV's answer?

Peter Mortensen · Accepted Answer · 2021-09-26 21:22:38Z

2

You can use GET in the form's action parameter, which I use whenever I make a login/register combined page.

For example: action="loginregister.php?whichform=loginform"

edited Sep 26, 2021 at 21:22

Peter Mortensen

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answered Oct 25, 2015 at 11:08

Elttob

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1 Comment

Peter Mortensen Over a year ago

Re "GET": Isn't it customary to use "get" (lowercase) (not a rhetorical question)?

Peter Mortensen · Accepted Answer · 2021-09-26 21:50:06Z

1

I had a similar problem which brought me to this question. I reviewed all the preceding answers, but ultimately I ending up figuring out my own solution:

<form name="ctc_form" id="ctc_form" action='' method='get'>

    <input type="hidden" name="form_nm" id="form_nm">

    <button type="submit" name="submit" id="submit" onclick="document.getElementById('form_nm').value=this.closest('form').name;">Submit</button>

</form>

It seamlessly and efficiently accomplishes the following:

Passes the form name attribute via a hidden input field, without using the fallible value attribute of the submit button.
Works with both GET and POST methods.
Requires no additional, independent JavaScript.

edited Sep 26, 2021 at 21:50

Peter Mortensen

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answered Jun 24, 2019 at 12:09

James Anderson Jr.

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1 Comment

Frazer Over a year ago

Hi James thanks for your answer it was helpful to me. Could you please expand on why the submit button's value is fallable, thank you.

Peter Mortensen · Accepted Answer · 2016-11-22 22:37:08Z

0

You could just give a name to the submit button and do what needs to be done based on that. I have several forms on a page and do just that. Pass the button name and then if button name = button name do something.

edited Nov 22, 2016 at 22:37

Peter Mortensen

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answered Apr 14, 2016 at 1:44

Adrian Fischer

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Comments

Peter Mortensen · Accepted Answer · 2021-09-26 21:07:08Z

0

Only the names of the form fields are submitted, but the name of the form itself is not. But you can set a hidden field with the name in it.

edited Sep 26, 2021 at 21:07

Peter Mortensen

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answered May 10, 2009 at 20:13

Gumbo

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