if (ereg('^[[:alnum:]]+$', $data)) {
echo '$data contains only letters and/or numbers';
} else {
echo '$data contains characters other than letters and /or numbers.';
}

and if you want to add characters to allow, like an underscore for instance, add a pipe and the _ after the [:alnum:], like so:

if (ereg('^[[:alnum:]|_]+$', $data)) {
echo '$data contains only letters and/or numbers';
} else {
echo '$data contains characters other than letters and /or numbers.';
}

hope that helps

with "s"
3#3 is allowed

with "i"
3#3 is not

…duh… I'm so lost.
I'll send you some Reese's Pieces to give to your friend… (Does he like Tiaras? LOL!)

I pinged him and asked for an explanation that's readable in English, and here's his response:

"The $ matches the end of the line. The i is a flag meaning 'case insensitive match.' Likewise, the ^ at the beginning matches the beginning of the line. It won't match (allow) any strings that contain spaces or whatever at the beginning/end.

"One could argue that you could use /^\w+$/ instead, but then it'd match (allow) the underscore character as well."

Personally, I hate regexes. They drive me insane on a regular basis. I bribe Gareth with Reese's Pieces (which are hard to get and expensive in Britain) to get help for regex issues like this.

the difference between what you were doing with the preg_match, and what I was doing… is the last part… the "+$/i"… I had been using "+$/s" (which didn't catch special charcters in the middle)

Can you tell me whats going on there? What does the "i" or "s" mean?

That's why I got into the whole check every character thing…

function is_alphanumeric($test) {
return (preg_match("/^[a-z0-9 ]+$/i", $test));
}

Run it like this:

if ( !is_alphanumeric($submitted_variable) ) {
  # fire error stuff
}

It's probalby going to be some form of this function:
ereg() but the question is what do I put in there to deny all special characters…