How to Check if a String is Null in PHP

PHP is a dynamic scripting language that is frequently used in the web development industry to create dynamic web pages. PHP programming frequently involves determining whether a string variable contains a null value.

This tutorial will show you how to use a variety of PHP functions to ascertain whether a string is null, so you can manage data efficiently and improve the functionality of your web applications.

Understanding Null in PHP:

Before delving into the strategies, it is imperative to comprehend what PHP null indicates. 

A variable that has been intentionally set to null or has no value at all is denoted by the PHP variable null. Understanding the difference between a null value and an empty string (' ') is crucial. 

A null value denotes the complete missing of any value, although an empty string still has a value in the absence of letters.

Using the is_null() Function:

is_null() is the easiest and most straightforward way to determine whether a string in PHP is null. When a variable is considered null, this function returns true; otherwise, it returns false.

<?php 

//determine for true value of the $str variable for null;

$str = true;

if (is_null($str))
{
	echo 'Variable str blank is blank';
}
else
{
	echo 'Variable str is not blank';
}

echo nl2br("\n");


// check for false value of the $str variable for null";

$str = false;

if (is_null($str))
{
	echo 'Variable str is empty' ;
}
else
{
	echo 'Variable str is not empty';
}

echo nl2br("\n");


// Check for null value of the $str variable for null";

$str = null;

if(is_null($str)) 
{
    echo "The string is null";
} 
else 
{
    echo "The string is not null";
}

?>

Output:

Variable str is not blank
Variable str is not empty
The string is null

Note: The nl2br() function places HTML line breaks ("br />") at the start of each new line ("\n").

Using empty() Function:

Using the empty() function is another way to see if any strings in PHP are null or empty. This function considers values like 0, false, ' ', array(), and null as empty in addition to checking for null.

Example:

Three variables ($var1, $var2, $var3) in this PHP application have values of 0, ' ', and null.

The empty() function is used to check whether the values of these variables are blank; if they are, the program returns true.

<?php

$var1 = 0;

$var2 = "";

$var3 = null;

$check1 = empty($var1);
$check2 = empty($var2);
$check3 = empty($var3);

echo "Result of all variables is shown below.<br /><br />";

if ($check1) 
{
	echo "true.<br>";
}

if ($check2) 
{
	echo "true.<br>";
}

if ($check3) 
{
	echo "true.<br>";
}

?>

Output:

Result of all variables is shown below.

true.
true.
true.

In this PHP program, we also check the variable value not blank using the empty() function.

<?php

// check variable value is not empty 

$newvar = 'hello';

if(empty($newvar))
{
	echo 'variable value is empty';
}
else
{
	echo 'variable value is not empty';
}

?>

Output:

variable value is not empty

Using Strict Comparison:

PHP has strict comparison operators (!== and ===) that compare data types in addition to values. Without mixing types, you may reliably determine whether a string is blank by using the strict comparison operator.

Example:

The == operator is used in this PHP program to determine whether the numerical values of the two variables match or not.

Return true if it was discovered; otherwise, return false.

<?php

//compare only numerical values using two variables

$var1 = 2;
$var2 = 5;

if($var1==$var2)
{
	echo "TRUE : Because both variable's values are same \n";
}
else
{
	echo "FALSE : Because both variable's values are not same \n";
}

?>

Output:

FALSE : Because both variable's values are not same

The == operator is used in this PHP example to determine whether the string values of the two variables are equal or not.

Return true if it was found; otherwise, return false.

<?php

//check to compare two string values

$var1 = "google";
$var2 = "google";

if($var1==$var2)
{
	echo "TRUE : Because both variables' string values are the same \n";
}
else
{
	echo "FALSE : Because both variables' string values are not same \n";
}

?>

Output:

TRUE : Because both variables' string values are the same

Checking with strlen() Function:

Using the strlen() function, which yields the string's length, provides another way to recognize nil or missing strings. A string's length of zero indicates that it is undefined or nothing.

Example:

In this PHP program, we check the $str variable value is not blank using the strlen() function.

The === operator determines whether the variable value is equal to zero or not.

If found then return null otherwise return not null.

<?php

$str = '';

if (strlen($str) === 0) 
{
    echo "The string is null.";
} 
else 
{
    echo "The string is not null.";
}

?>

Output:

The string is null.

In this PHP program, the $str variable holds the value of 'hello world', so the output shows the string is not null.

<?php

$str = "hello world"; 

if (strlen($str) === 0) 
{
    echo "The string is null.";
} 
else 
{
    echo "The string is not null.";
}

?>

Output:

The string is not null.

Conclusion:

In conclusion, a key component of web development is using PHP to handle empty strings. Functions such as is_null(), empty(), strict comparison, and strlen() allow you to precisely determine whether a string is blank and adjust the behavior of your program accordingly. Gaining knowledge of these techniques will enable you to develop PHP apps that are more reliable and error-free.

Frequently Asked Questions

Q: Can a variable be both null and empty in PHP?

Answer: No, a variable cannot be empty and null at the same time. A variable is said to have no value at all if it is null. On the other hand, an empty variable is not null even though it can have a value but no characters.

Q: What's the difference between == and === in PHP comparisons?

Answer: The equality operator in PHP, ==, handles type managing when comparing. The strict equality operator, ===, compares data types and values without any type of mixing. Use === when checking for a blank to prevent unexpected outcomes from type conversions.

Q: How do I assign a null value to a variable in PHP?

Answer: PHP's assignment operator = can be used to set a variable's value to null. $variable = null; for instance, sets the variable to null.

Q: Can I use null as a default parameter value in PHP functions?

Answer: In PHP functions, it is possible to set the default argument value to null. You can call the function without giving a value if a function argument has a default value of null. In the absence of a value, the parameter will be nil.

Q: Are there any performance considerations when using different methods to check for null in PHP?

Answer: In general, there are very few speed differences between different PHP techniques for verifying null. But because it eliminates type shifting and yields more accurate answers, stringent comparison (===) is somewhat faster than is_null() and empty(), especially when working with huge datasets.