Is there any problem with writing this regular expression like this?

No matter if I input English or Chinese, why does it always prompt that it is illegal?

<code>$reg1='/\w{20,100}/';
$a=str_replace(" ","",$_POST['name']);
if(preg_match($reg1, $a)){
                echo "合法";
              }else{
                echo "不合法";
              }</code>

Reply content:

No matter if I input English or Chinese, why does it always prompt that it is illegal?

<code>$reg1='/\w{20,100}/';
$a=str_replace(" ","",$_POST['name']);
if(preg_match($reg1, $a)){
                echo "合法";
              }else{
                echo "不合法";
              }</code>

<code class="php">$reg1='/^.{20,100}$/u';</code>

1. w can only match letters+numbers+underscores

2. If there is no ^ $ restriction, it will always be true as long as there are more than 20 characters, such as 1000 a's.

3. u modifier makes the lower version of php Chinese-friendly. I tested php7, and it doesn’t matter whether you add u or not.

<code>$reg1='/([\x{4e00}-\x{9fa5}]|\w){20,100}$/u';
</code>

You try it, Chinese is also available