search
HomeBackend DevelopmentPHP TutorialWhy does `$a == NULL` evaluate to true when `$a` is an empty string in PHP?

Why does `$a == NULL` evaluate to true when `$a` is an empty string in PHP?

NULL in PHP: When an Empty String Isn't Null

Consider the following PHP code:

<code class="php">$a = '';
if($a == NULL) {
  echo 'is null';
}</code>

Why does it output "is null" when $a is clearly an empty string? Is this a bug?

Understanding Equality and Identity

The key to understanding this behavior lies in the distinction between equality (==) and identity (===). In PHP, == checks if two operands have the same value, while === checks if they have the same value and type.

In the code above, $a is an empty string, which is a falsy value. In PHP, falsy values are treated as equal to NULL, false, 0, and empty arrays. Therefore, $a == NULL evaluates to true.

Using === to Check for NULL

To specifically check if a variable is NULL, use the identity operator (===):

<code class="php">if($variable === NULL) {...}</code>

Note the triple equals sign. By using ===, you ensure that the variable is not only falsy, but also of type NULL.

Conclusion

The empty string in PHP is not considered NULL. To explicitly check for NULL, use the identity operator (===). This distinction is crucial for ensuring accurate comparison and logic in your PHP code.

The above is the detailed content of Why does `$a == NULL` evaluate to true when `$a` is an empty string in PHP?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
11 Best PHP URL Shortener Scripts (Free and Premium)11 Best PHP URL Shortener Scripts (Free and Premium)Mar 03, 2025 am 10:49 AM

Long URLs, often cluttered with keywords and tracking parameters, can deter visitors. A URL shortening script offers a solution, creating concise links ideal for social media and other platforms. These scripts are valuable for individual websites a

Introduction to the Instagram APIIntroduction to the Instagram APIMar 02, 2025 am 09:32 AM

Following its high-profile acquisition by Facebook in 2012, Instagram adopted two sets of APIs for third-party use. These are the Instagram Graph API and the Instagram Basic Display API.As a developer building an app that requires information from a

Working with Flash Session Data in LaravelWorking with Flash Session Data in LaravelMar 12, 2025 pm 05:08 PM

Laravel simplifies handling temporary session data using its intuitive flash methods. This is perfect for displaying brief messages, alerts, or notifications within your application. Data persists only for the subsequent request by default: $request-

Build a React App With a Laravel Back End: Part 2, ReactBuild a React App With a Laravel Back End: Part 2, ReactMar 04, 2025 am 09:33 AM

This is the second and final part of the series on building a React application with a Laravel back-end. In the first part of the series, we created a RESTful API using Laravel for a basic product-listing application. In this tutorial, we will be dev

Simplified HTTP Response Mocking in Laravel TestsSimplified HTTP Response Mocking in Laravel TestsMar 12, 2025 pm 05:09 PM

Laravel provides concise HTTP response simulation syntax, simplifying HTTP interaction testing. This approach significantly reduces code redundancy while making your test simulation more intuitive. The basic implementation provides a variety of response type shortcuts: use Illuminate\Support\Facades\Http; Http::fake([ 'google.com' => 'Hello World', 'github.com' => ['foo' => 'bar'], 'forge.laravel.com' =>

cURL in PHP: How to Use the PHP cURL Extension in REST APIscURL in PHP: How to Use the PHP cURL Extension in REST APIsMar 14, 2025 am 11:42 AM

The PHP Client URL (cURL) extension is a powerful tool for developers, enabling seamless interaction with remote servers and REST APIs. By leveraging libcurl, a well-respected multi-protocol file transfer library, PHP cURL facilitates efficient execution of various network protocols, including HTTP, HTTPS, and FTP. This extension offers granular control over HTTP requests, supports multiple concurrent operations, and provides built-in security features.

12 Best PHP Chat Scripts on CodeCanyon12 Best PHP Chat Scripts on CodeCanyonMar 13, 2025 pm 12:08 PM

Do you want to provide real-time, instant solutions to your customers' most pressing problems? Live chat lets you have real-time conversations with customers and resolve their problems instantly. It allows you to provide faster service to your custom

Announcement of 2025 PHP Situation SurveyAnnouncement of 2025 PHP Situation SurveyMar 03, 2025 pm 04:20 PM

The 2025 PHP Landscape Survey investigates current PHP development trends. It explores framework usage, deployment methods, and challenges, aiming to provide insights for developers and businesses. The survey anticipates growth in modern PHP versio

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

SublimeText3 Linux new version

SublimeText3 Linux new version

SublimeText3 Linux latest version

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools