如何检查给定字符串是否有效正则表达式？ [重复]

Question

Possible Duplicate:
Test if a regular expression is a valid one in PHP

 <?php 

    $subject = "PHP is the web scripting language of choice.";    
    $pattern = 'sssss';

    if(preg_match($pattern,$subject))
    {
        echo 'true';
    }
    else
    {
        echo 'false';
    }

?>

The above code gives me warning because the string $pattern is not a valid regular expression.

If I pass valid regular expression then it works fine.....

How can i check $pattern is valid regular expression?

Answer 1

You can just wrap preg_match with try catch, and consider result false, if it throws exception.

Anyway, you can take a look at regular expression to detect a valid regular expression.