How to validate pattern in input string?

Question

如果我有一个网页，并且希望确保用户输入的变量只有字母（上下），数字和破折号且长度必须恰好为20个字符，那么如何执行呢？

Answer 1

This is pretty easy to do using regular expressions:

echo preg_match('/^[0-9a-zA-Z\-]{20}$/', 'abcd');
0
echo preg_match('/^[0-9a-zA-Z\-]{20}$/', 'abcdefghijkmlnopqrst');
1

Answer 2

You can use regular expressions. See preg_match .

Your regular expression could look something like:

/^[A-Za-z0-9\-]{20}$/

or

/^[\w-]{20}$/

Answer 3

if you don't trust in regexp because of performance you may use the following, which will take longer:

function checkalphanum($str){
    $allowed = "0123456789abcdefghijklmnopqrstuvwxyz_-ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    if(strlen($str) == 20){ return false;}
    for($i=0; $i < count($str); $i++){
        if(strpos($allowed, substr($str, $i, 1)) == -1){
            return false;
        }
    }
    return true;
}