Determine if a character is alphabetic

Question

Hello,

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

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...
}

Answer 2

You can try:

preg_match('/^[a-zA-Z]$/',$input_char);

The return value of the above function is true if the $input_char contains a single alphabet, else it is false. You can suitably make use of return value.

Answer 3

preg_match('/^[a-zA-Z]$/', $var_vhar);

Method will return int value: for no match returns 0 and for matches returns 1.

Answer 4

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 5

I'd use ctype, as Nick suggested,since it is not only faster than regex, it is even faster than most of the string functions built into PHP. But you also need to make sure it is a single character:

if (ctype_alpha($ch) && strlen($ch) == 1) {
    // Accept
} else {
    // Reject
}