Filters in PHP

        Checking strings is the most common function in programs . For example, meeting such a scene , Verify that the string matches ip Address format . There are usually two ways ：

     （1） Writing a ip Address verification function

     （2） Regular expressions

        In the use of C When language deals with such problems , It usually takes more than ten minutes to write a verification function . Using a language that supports regularity (php、C++11 etc. ) When dealing with such problems , Regular . But regularization is difficult to use , And it's not intuitive to read .（ This in no way means that regularity is not important ）. Sometimes they just want to quickly solve the immediate problems , So what should we do ？ At least in the php We can use filters in .

        The filter is used through the filter function , Such as filter_var Used to judge whether a variable meets the requirements

      Here is a paragraph to verify IP And whether the email is valid ：

   <?php

    $ip="192.168.0.222";
    $is_ip=filter_var($ip,FILTER_VALIDATE_IP);
    var_dump($is_ip);
    $mail="[email protected]";
    $is_mail=filter_var($mail,FILTER_VALIDATE_EMAIL);
    var_dump($is_mail);
   ?>

      This is better than checking the string yourself or Regularization is much more convenient ~

      php There are three types of filters in ： with VALIDATE The typeface filter only checks if the string is valid , Does not change the state of the string . with SANITIZE The filter of will delete the sub strings that do not meet the requirements , The third is FILTER_CALLBACK. That is, use your own callback function for verification .

      stay w3cschool There is an on-line website of form , A detailed list of php Functions of filters and filter functions in .

      PS： Filter in PHP5.2 Later versions default to , Previous versions need to install extensions to use . The filter is easy to use , But its function is still limited , In the face of specific needs , And string Library 、 Regular combination .