Detect whether a string contains a single of double quote(s) PHP?

[Andy]

So i want to detect whether a string has a ' or " in it. Idon't want to strip the ' or " as i could uses addslashes to do so i just need a function that will detect if they are in the string i can then send the input back saying please enter a valid username etc...and exit(); the script.

 

[DzSoundNirvana]

strstr()

if(strstr($_POST['key_name'], ''') || strstr($_POST['key_name'],'"')){
echo "Please enter in a valid username";
}