PHP: is_string function not working properly in my validation form

Question

Can somebody help me? I am starting to learn PHP and i am trying to validate my username and password. it should only input characters, otherwise it will prompt validation error. However, even if i entered numbers, my form is still successful. I've used is_string function to validate but it seems it's not working.

Here's my code:

<?php

    if(isset($_POST['submit'])) {
        $username = $_POST['username'];
        $password = $_POST['password'];
        if(!is_string($username) && !is_string($password)) {
            echo "Error! Please input characters only.";
        }
        else {
            echo "successful";
        }
    }
    else {
            $username = "";
            echo "Please log in.";
    }
?>

<!DOCTYPE html>
<html>
<head>
    <title> First Page </title>
    <meta charset="UTF-8"/>
</head>
<body>

    <form action="basic.php" method="POST">
    Username: <input type="text" name="username" value="<?php $username ?>" /> <br/>
    Password:   <input type="password" name="password" /> <br/>
    Submit: <input type="submit" name="submit" value="Submit" />
    </form>


</body>
</html>

data submitted from text boxes are strings even if it's all numbers — Memor-X
– Memor-X, Commented Sep 6, 2016 at 6:52
Why would you want to restrict your password like that? Assuming you mean || instead of &&. — jeroen
– jeroen, Commented Sep 6, 2016 at 6:55
i think you should use || instead of && to validate the input — FullStack
– FullStack, Commented Sep 6, 2016 at 6:57

Bart Friederichs · Accepted Answer · 2016-09-06 06:53:34Z

1

is_string only check the type of variable you are using. And, in this case, both variables are indeed strings, as they should be.

If you want to validate, you could use regular expression matching, for example:

if(preg_match( '/^[0-9]+$/', $string )) {
    // all numbers
}

Be warned though, regular expressions can be daunting to the beginner.

answered Sep 6, 2016 at 6:53

Bart Friederichs

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Pruthviraj Chudasama · Accepted Answer · 2016-09-06 07:07:46Z

1

replace this code with your code its solve your problem

if(preg_match('/[^A-Za-z]/', $username) && preg_match('/[^A-Za-z]/', $password)) 
{
  echo "Error! Please input characters only.";
}
else
{
  echo "successful";
}

answered Sep 6, 2016 at 7:07

Pruthviraj Chudasama

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FrankSunnyman · Accepted Answer · 2016-09-06 07:03:49Z

0

The $_POST['username'] could be '1234' which does indeed contain numbers, but is still considered a string. Since is_string() only checks for the type of a variable it is working as expected.

For validation you could use a regular expression (regex) but I think that's a bit overkill and performance-wise not the best option. A native function like ctype_alpha might fit better.

answered Sep 6, 2016 at 7:03

FrankSunnyman

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6 Comments

Bart Friederichs Over a year ago

Performance is hardly an issue here. Also, using a regular expression will give you more flexibility in the future (what if you want to allow number in the future, for example). In addition to that, ctype_alpha will also denote strings with diacritics (e.g. "áé") as not-alphabetic.

Jacob Rosta Over a year ago

I understand that is_string function only check the type of the variable. but when i try other way of using this, i get the expected results. Only when i am using form input that i do not. Please see this sample where i can get the expected results: <?php $number = 3; if(!is_string($number)) { echo "Error! Please input characters only."; } else { echo "successful"; } ?>

FrankSunnyman Over a year ago

@BartFriederichs the OP stated he was starting to learn PHP so using a regex right away might be a bit too confusing.

FrankSunnyman Over a year ago

@JacobRosta That's probably because your formdata is '3' (a string, note the quotation marks) as opposed to 3 (integer). You could use the function gettype() on your formdata to get the type of variable.

Jacob Rosta Over a year ago

then why do textboxes are strings even if it's numbers?

|

Eric_ph · Accepted Answer · 2016-09-06 07:15:03Z

0

Use preg_match to validate the username, and password for your purpose. For example at hiteachers.com, I only allow letters (enable case-insensitive mode), a period (as in an initial),an apostrophe, a space, and the dash, and the value should be within the range of 4 to 20 characters long, you can use (preg_match ('/^[\w \'.-]{4,20}$/i', $_POST['username'])).

answered Sep 6, 2016 at 7:15

Eric_ph

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