


PHP 5 ways to determine whether an array is empty_PHP Tutorial
5 major ways to determine whether an array is empty in PHP
1. isset function: determine whether the variable has been initialized
Note: It does not determine whether the variable is empty, and can be used to determine whether the elements in the array have been defined
Note: When using isset to determine whether an array element has been initialized, its efficiency is about 4 times higher than array_key_exists
<ol class="dp-c"><li class="alt"><span><span><?php </span></span></li><li><span><span class="vars">$a</span><span> = </span><span class="string">''</span><span>; </span></span></li><li class="alt"><span><span class="vars">$a</span><span>[</span><span class="string">'c'</span><span>] = </span><span class="string">''</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (!isset(</span><span class="vars">$a</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$a 未被初始化'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="keyword">if</span><span> (!isset(</span><span class="vars">$b</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$b 未被初始化'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (isset(</span><span class="vars">$a</span><span>[</span><span class="string">'c'</span><span>])) </span><span class="func">echo</span><span> </span><span class="string">'$a 已经被初始化'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="comment">// 显示结果为</span><span> </span></span></li><li><span><span class="comment">// $b 未被初始化</span><span> </span></span></li><li class="alt"><span><span class="comment">// $a 已经被初始化</span><span> </span></span></li></ol>
2. empty function: detect whether the variable is "empty"
Note: Any uninitialized variable, a variable with a value of 0 or false or an empty string "" or null, an empty array, or an object without any attributes will be judged as empty==true
Note 1: Uninitialized variables can also be detected as "empty" by empty
Note 2: empty can only detect variables, not statements
<ol class="dp-c"><li class="alt"><span><span><?php </span></span></li><li><span><span class="vars">$a</span><span> = 0; </span></span></li><li class="alt"><span><span class="vars">$b</span><span> = </span><span class="string">''</span><span>; </span></span></li><li><span><span class="vars">$c</span><span> = </span><span class="keyword">array</span><span>(); </span></span></li><li class="alt"><span><span class="keyword">if</span><span> (</span><span class="func">empty</span><span class="keyword">empty</span><span>(</span><span class="vars">$a</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$a 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="func">empty</span><span class="keyword">empty</span><span>(</span><span class="vars">$b</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$b 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="keyword">if</span><span> (</span><span class="func">empty</span><span class="keyword">empty</span><span>(</span><span class="vars">$c</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$c 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="func">empty</span><span class="keyword">empty</span><span>(</span><span class="vars">$d</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$d 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li></ol>
3. var == null function: determine whether the variable is "empty"
Note: Variables and empty arrays whose value is 0 or false or empty string "" or null will be judged as null
Note: The significant difference from empty is that var == null will report an error when the variable is not initialized.
<ol class="dp-c"><li class="alt"><span><span><?php </span></span></li><li><span><span class="vars">$a</span><span> = 0; </span></span></li><li class="alt"><span><span class="vars">$b</span><span> = </span><span class="keyword">array</span><span>(); </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="vars">$a</span><span> == null) </span><span class="func">echo</span><span> </span><span class="string">'$a 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="keyword">if</span><span> (</span><span class="vars">$b</span><span> == null) </span><span class="func">echo</span><span> </span><span class="string">'$b 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="vars">$c</span><span> == null) </span><span class="func">echo</span><span> </span><span class="string">'$b 为空'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="comment">// 显示结果为</span><span> </span></span></li><li><span><span class="comment">// $a 为空</span><span> </span></span></li><li class="alt"><span><span class="comment">// $b 为空</span><span> </span></span></li><li><span><span class="comment">// Undefined variable: c</span><span> </span></span></li></ol>
4. is_null function: detect whether the variable is "null"
Note: When the variable is assigned a value of "null", the detection result is true
Note 1: null is not case sensitive: $a = null; $a = NULL makes no difference
Note 2: The detection result is true only when the value of the variable is "null". 0, empty string, false, and empty array are all detected as false
Note 3: When the variable is not initialized, the program will report an error
<ol class="dp-c"><li class="alt"><span><span><?php </span></span></li><li><span><span class="vars">$a</span><span> = null; </span></span></li><li class="alt"><span><span class="vars">$b</span><span> = false; </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="func">is_null</span><span>(</span><span class="vars">$a</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$a 为NULL'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="keyword">if</span><span> (</span><span class="func">is_null</span><span>(</span><span class="vars">$b</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$b 为NULL'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li><span><span class="keyword">if</span><span> (</span><span class="func">is_null</span><span>(</span><span class="vars">$c</span><span>)) </span><span class="func">echo</span><span> </span><span class="string">'$c 为NULL'</span><span> . </span><span class="string">""</span><span>; </span></span></li><li class="alt"><span><span class="comment">// 显示结果为</span><span> </span></span></li><li><span><span class="comment">// $a 为NULL</span><span> </span></span></li><li class="alt"><span><span class="comment">// Undefined variable: c</span><span> </span></span></li></ol>
5. var === null function: detect whether the variable is "null", and the type of the variable must also be "null"
Note: When a variable is assigned a value of "null" and the type of the variable is also "null", the detection result is true
Note 1: When judging "null", equal to is_null has the same effect
Note 2: When the variable is not initialized, the program will report an error
Summary:
In PHP, "NULL" and "empty" are two concepts.
isset is mainly used to determine whether a variable has been initialized
empty can judge variables with values of "false", "empty", "0", "NULL", and "uninitialized" as TRUE
is_null only evaluates variables with a value of "NULL" as TRUE
var == null Judges variables with values of "false", "empty", "0", and "NULL" as TRUE
var === null Only variables with a value of "NULL" are judged as TRUE
Note: When judging whether a variable is really "NULL", is_null is mostly used to avoid interference from "false", "0" and other values.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

If you are an experienced PHP developer, you might have the feeling that you’ve been there and done that already.You have developed a significant number of applications, debugged millions of lines of code, and tweaked a bunch of scripts to achieve op

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.
