How do I add php if statement into my form - php

Question

I have an update form where users can update their information, but some of the information should not be able to be updated if it already has a value.
From what I understand you must put php code outside the form tags so how would the form know if the database field has a value or not? Would this work below im guessing it won't
<form>
<?php
if (empty($user_data['fieldName'])) {
echo '<label>field name</label>
<input type="text" name="fieldName">';
}
?>
</form>
Does anyone know a way around this? Or how would i check before the field is displayed in the update area?

Answer 1

This part of the code is correct, you may have a problem when assigning the user data in the array $user_data.
An alternative would be to simply disable the input text, that way you could display information to the user without letting him change it.
<form>
<?php
$disabled = "";
if (empty($user_data['fieldName'])) {
$disabled = 'disabled="disabled"'
} ?>
<label>field name</label>
<input type="text" name="fieldName" <?php echo $disabled; ?>/>
</form>

Answer 2

Of course you can do in that way but you should check on the server too if not update exist
Also the most readable way of do this is using alternate php syntax like this
<form>
<?php if (empty($user_data['fieldName'])): ?>
<label>field name</label>
<input type="text" name="fieldName">
<?php endif; ?>
</form>
in that way you can see colors of your html code
see this link,
Alternative php syntax
the doc is for codeigniter but is applicable on clean php
Sorry for my bad english :)

Answer 3

You should have a presentation code, like this :
<form>
<label>field name</label>
<input type="text" name="fieldName" <?=!empty($user_data['fieldName'])?'disabled="disabled"':''?>>
</form>
And a script to update, where you must check if value is set before updating.

Answer 4

As mentioned in a comment, you can put PHP anywhere in a *.php file, so long as it is enclosed in the correct opening and closing tags.
That said, this is a two-sided process:
In the form I would suggest simply disabling the input, so the data is shown, but is not modifiable:
<form>
<label>field name</label>
<input type="text" value="<?php echo addslashes($user_data['fieldName']) ?>" name="fieldName" <?php if(!empty($user_data['fieldName'])) { echo 'disabled="disabled"; } ?> />
</form>
<?php /* Off the top of my head I can not remember how exactly to escape this
form value, it may be `htmlspecialchars`, but it eludes me in the immediate
moment. Sorry. */ ?>
And on your server-side, where you handle the form post data, you will want to double-check that someone didn't forge the data:
if(!empty($user_data['fieldName']) && !empty($_POST['fieldName'])) {
unset($_POST['fieldName']);
}
This way you avoid people modifying the form structure on the client to forge data into your system. You should always do similar checks.