SQL Injection, prevent Options

[nerotech]

Hello,

I'm not too experienced with php, more of a c++ person..
I was wondering if the code i've developed here is sufficient enough to prevent SQL Injections?

CODE

public function verify(Creg $reg) {

$reg->Username = strtolower(strip_tags(stripslashes(trim($reg->Username))));

//validate characters
if(preg_match("/^[a-z0-9]{1}[a-z0-9_-]{1,19}$/",$reg->Username)) {
//db query, reject username, or validate and move on
}
else {
$this->Error[] = '-Invalid characters, or username too short.<br />';
}
#contnue...
}