PHP string validation

Question

I have been trying too use PHP to validate my form. The form asks users to enter details which will then get entered into a table in a database once the form has been validated. I have a first name field in the form and I am trying to validate it to make sure that it has a value entered (compulsory field) and should only contain alphabetic characters or a hyphen(-) character.

Here is what i have so far:

<?php
if (isset($_POST["submit"])) {

$flag = false;
$badchar = "";
$string = $_POST["fname"];
$string = trim($string);
$length = strlen($string);
$strmsg = "";

if ($length == 0) {
$strmsg = '<span class="error"> Please enter your first name</span>';
$flag = true;}
else {
for ($i=0; $i<$length;$i++){
    $c = strtolower(substr($string, $i, 1));
    if (strpos("abcdefghijklmnopqrstuvwxyz-", $c) == false){
        $badchar .=$c;
        $flag = true;
    }
}
if ($flag) {
    $strmsg = '<span class="error"> The field contained the following invalid characters: $badchar</span>';}
}
if (!$flag) {
    $strmsg = '<span class="error"> Correct!</span>';}
}
?>

<h1>Customer Information Collection <br /></h1>

<form method="POST" action="<?php echo $_SERVER["PHP_SELF"];?>" id="custinfo" >
<table>
<tr>
    <td><label for="custid">Customer ID (integer value): </label></td>
    <td><input type="text" id="custid" name="custid" value="<?php echo $temp ?>" size=11 /><?php echo $msg; ?></td>
</tr>

<tr>
    <td><label for="customerfname">Customer First Name: </label></td>
    <td><input type="text" id="fname" name="fname" size=50/><?php echo $strmsg; ?></td>
</tr>

The problem I am having is that when I enter a correct string (e.g. John) it still gives me the error "The field contained the following invalid characters: $badchar", also when an incorrect character is entered i would like for it to display the incorrect character in the place of $badchar in the error message but instead it just displays "The field contained the following invalid characters: $badchar".Is there a way to do that?

Any help with these problems would be really appreciated.

RMcLeod · Accepted Answer · 2013-05-03 16:32:00Z

1

Your problem is that you have done == false and strpos can return 0 (the index of the first character) which evaluates as false. Swap == false with === false which checks that the value is boolean false and not a value that evaluates to false. See the 'Return Values' section at http://php.net/manual/en/function.strpos.php

To print the value of $badchar change the line to

$strmsg = '<span class="error"> The field contained the following invalid characters: '.$badchar.'</span>';

This will concatenate the variable into your string

answered May 3, 2013 at 16:32

RMcLeod

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Sam Dufel · Accepted Answer · 2013-05-03 16:34:45Z

0

You have a few problems with your code.

strpos() returns either 0-based index of the location of your search string in the text, OR it returns false. You need to use the === operator to check the results; otherwise, a 0 result will be interpreted as false.

In your error string, you're seeing:
The field contained the following invalid characters: $badchar

In php, variables are only parsed out in double-quoted strings. Since you're using single quotes, it'll just echo the actual text you entered, not the contents of the variable. You can switch the double and single quotes in your string to fix it.

answered May 3, 2013 at 16:34

Sam Dufel

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