Wednesday, September 14, 2016

Understanding the Difference Between isset(), empty(), is_empty() and unset() functions in PHP

isset() function in PHP: 

As the name suggests the isset() function in PHP checks whether the variable 'is set' or not. To be more clear this is what happens when this function is called:
  •  Checks whether the variable is declared or exists or set or not. It returns TRUE or 1 if the variable is not NULL, not an Empty String represented by '' or an Undeclared variable.

empty() function in PHP: 

The empty() function in PHP returns TRUE or 1 in the following cases:
  1. if the variable is undeclared
  2. if the variable is assigned zero. Example $high = 0;
  3.  if the variable is assigned an Empty string or declared NULL. Example: $high= ''; or $high = NULL;

is_null() function in PHP:

As the name suggests, the is_null() function checks whether a variable is NULL or not. This holds TRUE if:
  1. variable is not declared
  2. variable is declared as NULL. Example: $high = NULL;
Note: '' empty string is not NULL.

    unset():  

    You can wipe a variable out of existence using unset().


    Handy Usage: These functions are handy when you need to make sure that the user filled out the appropriate fields in the form.

    Example:

     <?php   
      // Experimenting with isset(), empty() & is_null()   
     // Comment/Uncomment each condition below and test  
      // $high = '';   
      // $high = NULL;   
      // $high = 0;   
      // $high = 'hello';   
      echo '$high = '.$high.'<br />';   
      echo 'isset($high) = '.isset($high).'<br />';   
      echo 'empty($high) = '.empty($high).'<br />';   
      echo 'is_null($high) = '.is_null($high).'<br />';   
      ?>   
    

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