A brief discussion on the differences between isset(), empty(), and is_null() in PHP

In PHP, isset(), empty() and is_null() can all be used to test the value of a variable, so what are the differences between them? The following article will compare these three functions and understand their differences.

#Let’s start with some definitions.

• isset() : You can use isset() to determine whether a variable is declared, and null is different.

• empty() : It is used to determine if a variable exists and the value of the variable has not evaluated to false.

• is_null() : This function is used to check whether a variable is null.

PHP isset() vs empty()

As we can see from the definition Yes, if we previously defined the variable and set its value to something other than NULL, then isset() will return true. This can include 0, an empty string, or false. On the other hand, empty() returns true whenever the value of a variable is set to false. We call these values ​​"false values". Examples of error values ​​include: 0, the empty string "" and the string "0", the empty array NULL, and of course Has boolean value false. One similarity between

isset() and empty() is that they are both language constructs and therefore cannot be called using variable functions.

The code snippet below should explain the difference between the two.

<?php

$fruit = &#39;&#39;;

if(isset($fruit)) {
    echo &#39;Do you like &#39;.$fruit.&#39;?&#39;;
}
// Output:  Do you like ?

if(!empty($fruit)) {
    echo &#39;Do you like &#39;.$fruit.&#39;?&#39;;
}
// No Output

?>

Please note that empty() can be written using the isset() function.

<?php

function my_empty($x) {
  return !isset($x) || $x == false
}

Of course, it's often easier to just use the built-in empty() function.

PHP isset() vs is_null()

If the value of a variable is explicitly set to NULL, then the is_null() function returns true. Otherwise, it just returns false. On the other hand, isset() will return true whenever a variable is defined and its value is not NULL.

Here is a basic example to illustrate the difference between them.

<?php

$fruit = NULL;

if(isset($fruit)) {
    echo &#39;Do you like &#39;.$fruit.&#39;?&#39;;
}
// No Output

if(is_null($fruit)) {
    echo &#39;There is no fruit.&#39;;
}
// Output: There is no fruit.

?>

PHP empty() vs is_null()

If the value of a variable is evaluated to false, the empty() function will return true. This may mean the empty string, NULL, the integer 0, or an array with no elements. On the other hand, is_null() will return true only if the value of the variable is NULL.

Here is a basic example to illustrate the difference between them.

<?php

$fruit = NULL;

if(isset($fruit)) {
    echo &#39;Do you like &#39;.$fruit.&#39;?&#39;;
}
// No Output

if(is_null($fruit)) {
    echo &#39;There is no fruit.&#39;;
}
// Output: There is no fruit.

?>

Important Things to Remember

There are two tips you can use to write cleaner code and avoid errors in the future.

1. Unlike empty() and is_null(), you can pass multiple values ​​to isset() at the same time Check if any of them are undefined or set to NULL. In this case, isset() will only return true if none of the passed values ​​are NULL.

2.2. Do not use == to check whether a value is NULL. This will give a false positive to values ​​like the empty string that evaluate to false.

Recommended learning: "PHP Video Tutorial"

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