Determine if a character is alphabetic

Question

Having problems with this.

Let's say I have a parameter composed of a single character and I only want to accept alphabetic characters. How will I determine that the parameter passed is a member of the latin alphabet (a–z)?

By the way Im using PHP Kohana 3.

Thanks.

Answer 1

http://php.net/manual/en/function.ctype-alpha.php

<?php
    $ch = 'a';
    if (ctype_alpha($ch)) {
        // Accept
    } else {
        // Reject
    }

This also takes locale into account if you set it correctly.

EDIT: To be complete, other posters here seem to think that you need to ensure the parameter is a single character, or else the parameter is invalid. To check the length of a string, you can use strlen(). If strlen() returns any non-1 number, then you can reject the parameter, too.

As it stands, your question at the time of answering, conveys that you have a single character parameter somewhere and you want to check that it is alphabetical. I have provided a general purpose solution that does this, and is locale friendly too.

Answer 2

Use the following guard clause at the top of your method:

if (!preg_match("/^[a-z]$/", $param)) {
    // throw an Exception...
}

If you want to allow upper case letters too, change the regular expression accordingly:

if (!preg_match("/^[a-zA-Z]$/", $param)) {
    // throw an Exception...
}

Another way to support case insensitivity is to use the /i case insensitivity modifier:

if (!preg_match("/^[a-z]$/i", $param)) {
    // throw an Exception...
}