The difference between empty and isset in PHP for parameter structure and empty () and isset () _php instance

No more nonsense to say, directly to everyone paste code.

<?php
  class test{}
  $a 1 = null;
  $a 2 = "";
  $a 3 =
  $a 4 = 0;
  $a 5 = ' 0 ';
  $a 6 = false;
  $a 7 = array ();
  var $a 8;
  $a 9 = new test ();
  for ($i =1; $i <=9 $i + +) {
    $s = ' a '. $i;
    Echo $i. ":";
    Var_dump (Isset ($ $s));
    echo ' <br/> ';
  }
  echo ' <br/> ';
  for ($i =1; $i <=9 $i + +) {
    $s = ' a '. $i;
    Echo $i. ":";
    Var_dump (Empty ($ $s));
    echo ' <br/> ';
  }

The difference between empty () and Isset () in ps:php

For beginners in PHP, the difference between empty () and isset () is hard to figure out, and it's really hard to figure out what their differences are.

Let's say what they have in common:

Can be used to determine whether a variable is empty;

Returns a Boolean type, that is true or false.

Here's a specific distinction between their usage:

Isset () is used to detect whether a variable is set and can only be used for a variable, because passing any other parameter will result in a parse error. To detect if a constant is set, use the defined () function. If you have freed a variable using unset (), it will no longer be isset (). If you use Isset () to test a variable that is set to NULL, it returns FALSE. (Note that a null byte ("") is not equivalent to the null constant of PHP)

Empty () is used to check whether a variable is empty.

The biggest difference between them is that for 0 of the judgment, if the empty judge will be considered empty, with isset is considered not empty, for example:

<?php
     var $a =0;
      Empty ($a) returns True
      if (empty ($a)) {
         echo evaluates to null
      }
     //isset ($a) returns True
      if (isset ($a)) {
         echo " Judging result is not empty "

      }
    ?>