Home Backend Development PHP Tutorial PHP中empty、isset、is_null差别

PHP中empty、isset、is_null差别

Jun 13, 2016 am 11:01 AM
empty false isset null true

PHP中empty、isset、is_null区别
empty

如果 变量 是非空或非零的值,则 empty() 返回 FALSE。换句话说,""、0、"0"、NULL、FALSE、array()、var $var、未定义; 以及没有任何属性的对象都将被认为是空的,如果 var 为空,则返回 TRUE。

isset

如果 变量 存在(非NULL)则返回 TRUE,否则返回 FALSE(包括未定义)。变量值设置为:null,返回也是false;unset一个变量后,变量被取消了。注意,isset对于NULL值变量,特殊处理。

is_null

检测传入值【值,变量,表达式】是否是null,只有一个变量定义了,且它的值是null,它才返回TRUE . 其它都返回 FALSE 【未定义变量传入后会出错!】.

Statement of this Website
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

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 ago By 尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PHP determines whether a specified key exists in an array PHP determines whether a specified key exists in an array Mar 21, 2024 pm 09:21 PM

This article will explain in detail how PHP determines whether a specified key exists in an array. The editor thinks it is very practical, so I share it with you as a reference. I hope you can gain something after reading this article. PHP determines whether a specified key exists in an array: In PHP, there are many ways to determine whether a specified key exists in an array: 1. Use the isset() function: isset($array["key"]) This function returns a Boolean value, true if the specified key exists, false otherwise. 2. Use array_key_exists() function: array_key_exists("key",$arr

What do undefined and null mean? What do undefined and null mean? Nov 20, 2023 pm 02:39 PM

In JavaScript, both undefined and null represent the concept of "nothing": 1. undefined represents an uninitialized variable or a non-existent property. When a variable is declared but no value is assigned to it, the value of the variable is undefined , when accessing properties that do not exist in the object, the returned value is also undefined; 2. null represents an empty object reference. In some cases, the object reference can be set to null to release the memory it occupies.

What is the difference between null and NULL in c language What is the difference between null and NULL in c language Sep 22, 2023 am 11:48 AM

The difference between null and NULL in C language is: null is a macro definition in C language, usually used to represent a null pointer, which can be used to initialize pointer variables, or to determine whether the pointer is null in a conditional statement; NULL is a macro definition in C language A predefined constant in , usually used to represent a null value, used to represent a null pointer, null pointer array or null structure pointer.

When to use null and undefined When to use null and undefined Nov 13, 2023 pm 02:11 PM

Both null and undefined indicate a lack of value or an undefined state. Depending on the usage scenario, there are some guiding principles for choosing to use null or undefined: 1. When you need to clearly indicate that a variable is empty or invalid, you can use null; 2. When a variable has been declared but not yet assigned a value, it will be set to undefined by default; 3. When you need to check whether a variable is empty or undefined, use the strict equality operator "===" to determine whether the variable is null or undefined. .

What is the difference between null and undefined What is the difference between null and undefined Nov 08, 2023 pm 04:43 PM

The difference between null and undefined is: 1. Semantic meaning; 2. Usage scenarios; 3. Comparison with other values; 4. Relationship with global variables; 5. Relationship with function parameters; 6. Nullability check; 7. Performance considerations; 8. Performance in JSON serialization; 9. Relationship with types. Detailed introduction: 1. Semantic meaning, null usually means knowing that this variable will not have any valid object value, while undefined usually means that the variable has not been assigned a value, or the object does not have this attribute; 2. Usage scenarios, etc.

PHP function introduction—empty(): Check whether the variable is empty PHP function introduction—empty(): Check whether the variable is empty Jul 25, 2023 am 10:23 AM

PHP function introduction—empty(): Check whether a variable is empty. In PHP programming, it is often necessary to judge a variable. It is a common requirement to judge whether a variable is empty. PHP's built-in empty() function is used to check whether the variable is empty. This article will introduce the usage of the empty() function and provide some practical code examples. The usage of the empty() function is very simple, it accepts one parameter and returns a Boolean value. When the value of the parameter is one of the following situations, the empty() function

Detailed explanation of the meaning of true in PHP functions Detailed explanation of the meaning of true in PHP functions Mar 16, 2024 am 08:57 AM

Detailed explanation of the meaning of true in PHP function In PHP, true is a Boolean value, representing the state of "true" or "yes". Using true in a function is usually used to express that a condition is true or to return a success status. This article will explain in detail the meaning of true in PHP functions from different perspectives, and give specific code examples. 1. Conditional judgment when true is returned: In PHP functions, true is usually used in conditional judgment to indicate that the condition is true. For example: functioni

What does true mean in PHP function? What does true mean in PHP function? Mar 16, 2024 pm 12:12 PM

Title: What does true mean in PHP functions? In PHP programming, true represents true in a Boolean value, usually indicating the state of "true". When true is used in a function, it is usually used to determine whether a condition is true or to perform some operation. The following will use specific code examples to illustrate what true means in PHP functions. example:

See all articles