Why check both isset() and !empty() functions in PHP

isset() function is a built-in function in PHP that checks whether a variable has been set and is not NULL. This function also checks if the declared variable, array or array key has a null value, if so, isset() returns false, it returns true in all other possible cases.

Syntax:

bool isset( $var, mixed )

Parameters: This function accepts multiple parameters. The first parameter of this function is $var. This parameter is used to store the value of the variable.

Example:

<?php 
  
$num = &#39;0&#39;; 
  
if( isset( $num ) ) { 
    print_r(" $num is set with isset function <br>"); 
} 
  
// 声明一个空数组 
$array = array();  
    
echo isset($array[&#39;geeks&#39;]) ?  
&#39;array is set.&#39; :  &#39;array is not set.&#39;;  
?>

Output:

0 is set with isset function 
array is not set.

empty() function is a language construct used to determine whether a given variable is empty or NULL . ! The empty() function is the negation or complement of the empty() function. empty() function and! The isset() function is equivalent, but! The empty() function is equal to the isset() function.

Example:

<?php 
  
  
$temp = 0; 
  
if (empty($temp)) { 
    echo $temp . &#39; is considered empty&#39;; 
} 
  
echo "\n"; 
  
$new = 1; 
if (!empty($new)) { 
    echo $new . &#39; is considered set&#39;; 
} 
?>

Output:

0 is considered empty
1 is considered set

The reason for checking two functions:

isset() and! The empty() function is similar, both will return the same result. But the only difference is! The empty() function does not generate any warning or electronic notification when the variable does not exist. It's enough to use either function. By merging two functions into a program it causes time lapse and unnecessary memory usage.

Example:

<?php 

$num = &#39;0&#39;; 
  
if( isset ( $num ) ) { 
    print_r( $num . " is set with isset function"); 
} 
  
echo "\n"; 
  
$num = 1; 
  
if( !empty ( $num ) ) { 
    print_r($num . " is set with !empty function"); 
}

Output:

0 is set with isset function
1 is set with !empty function

Related recommendations: "PHP Tutorial"http://www.php.cn/ course/list/29.html

This article is an introduction to the reasons why it is necessary to check isset() and !empty() functions at the same time in PHP. I hope it will be helpful to friends in need!

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