ctype_alnum to validate alphanumeric characters of a string in PHP

$var="10af4g4"; // This is  alphanumeric
//$var="abc=123"; // This is not alphanumeric
//$var="123"; // This is  alphanumeric
//$var='xyz'; // This is  alphanumeric
//$var='123.56'; // This is not alphanumeric
//$var=123;  // This is not alphanumeric

if(ctype_alnum($var)){
	echo "<b>$var</b> This is  alphanumeric ";
}else{ 
	echo " <b>$var</b> This is not alphanumeric";
}

output

This is  alphanumeric

Syntax

bool ctype_alnum ( string $input_string )

$input_string : String to be checked.

ctype_alnum is a PHP filter function checks presence of all alphanumeric characters. It allows a to z characters and 0 to 9 numbers. Any thing other than this if present then it return FALSE.

You can change the value of the variable $var in above script and see the result. Decimal points are not allowed ( False ) in ctype_alnum.

We can check the form data input by users directly by using ctype_alnum function.

Here is one example.

if(ctype_alnum($_POST['var'])){
echo " This is alphanumeric ";
}else{ echo "this is not alphanumeric";}

Checking array elements

$ar=array('abc','as12',123,'ab#1','@12');
foreach ($ar as $var){
if(ctype_alnum($var)){
	echo " <b>$var</b>  is alphanumeric  ";
}else{ 
	echo " <b>$var</b> is NOT alphanumeric ";
}
echo "<BR>";
}

output

abc  is alphanumeric
as12  is alphanumeric  
123 is NOT alphanumeric 
ab#1 is NOT alphanumeric 
@12 is NOT alphanumeric

Removing blank space before using

It is better to use string function trim to remove blank space present at starting and ending of the variable before using it. Users some time add blank space and this goes wrongly as not alphanumeric variable. Here is the modified script to remove blank space.

<?Php
$var=$_POST['var'];
$var=trim($var); // remove space at starting and ending of variable. 
if(ctype_alnum($var)){
echo " This is alphanumeric ";
}else{ echo "this is not alphanumeric";}
echo "<br><br>";// 
if(!ctype_alnum($var)){
echo " Inside if <br>";
}
?>

Allowing blank space and &

Using str_replace() we can remove space and '&' ( without quotes ) and check. Here is the code.

$search  = array('&', ' ');
$replace = array('', '');

if(!ctype_alpha(str_replace($search,$replace,$string_var))){
echo "Data Error ";
exit;
}

For easy understanding here is the form to submit data to above script

<form method=post action='ctype_alnck.php'>
<input type=text name=var>
<input type=submit value=submit>
</form>

Here if you want to check only numeric numbers then better to use is_numeric() function.
STRING REFERENCE Check for only alphabetic characters by ctype_alpha() Check for all lower or upper Check for at least one lower case or upper case
ctype()

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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Adan	06-12-2014
Well I am using this very same thing but when I submit the form I get the error although I am submitting alphanumerical usernames, I have tried alpha, alphanumeric, and numeric I get the same error. if(!isset($username) or strlen($username) <3){ $msg=$msg."User id should be =3 or more than 3 char length<BR>"; $status= "NOTOK";} if(!ctype_alnum($username)){ $msg=$msg."User id should contain alphanumeric chars only<BR>"; $status= "NOTOK";} Any ideas why it keeps throwing at me this error ? Any suggestions ? Thanks a lot

smo	06-12-2014
You may have to remove blank space from the variable. Sample code is added now.

Adan	07-12-2014
Yes thanks I have tried that, earlier but I had to rebuild the whole script with the exact same code, and now it is solved, no apparent reason whatsoever. Thanks again

rie	09-12-2014
good day, the function ctype_alnum for alphanumeric can't work for me.. just like when i change this code from if(!is_numeric($cat_id)){ echo "Data Error"; exit; } to $var=$_GET['cat']; if(ctype_alnum($var)){ echo " This is alphanumeric "; }else{ echo "this is not alphanumeric";} and i will change the value of cat_id int into a alphanumeric.. i cant see the value of a subcategory .. help me please .. thanks!

patrick	11-12-2014
i get the same error sir, but cant fix it .. here is my code .. help me please! Thanks in advance <?Php $cat=$_GET['cat']; $cat=trim($cat); if(ctype_alnum($cat)){ echo " This is alphanumeric "; }else{ echo "this is not alphanumeric";} echo "<br><br>"; if(!ctype_alnum($cat)){ echo " Inside if <br>"; } $quer2="SELECT DISTINCT ClientID,ClientID FROM creport order by ClientID"; if(isset($cat) and strlen($cat) > 0){ $quer="SELECT DISTINCT UnitId FROM ureport where ClientID=$cat order by ClientID"; }else{$quer="SELECT DISTINCT UnitId FROM ureport order by UnitId"; }

smo	12-12-2014
There is no reason why it should not work, check the value of $cat. Print the output and see are you getting the correct value or not.

ctype_alnum(): To check alphanumeric string

Checking array elements

Removing blank space before using

Allowing blank space and &

Subhendu Mohapatra