How to determine whether a variable is null in php

How to judge whether a variable is null in php: 1. Use is_null and isset functions to judge; 2. Use the equal or equal comparison operator to judge; 3. Use the empty method to judge.

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

PHP determines whether the variable is null

1. is_null and isset

Both functions can determine whether a variable is null. They have the same recognition of empty strings, 0, and false.

is_null = !isset();

The difference is that isset is a grammatical structure and is_null is a function. In terms of performance, the grammatical structure is relatively better. Therefore, it is recommended to use isset instead of is_null in many places

2, == and ===

In some cases, it is recommended to use isset to determine whether a variable is null

But syntactically, "whether a variable has been explicitly initialized" and "whether it is null" are different concepts. It is inappropriate to use isset in some scenarios, such as checking whether the return value of a function is null.

At this point you can use "==" and "===" to determine whether they are null

For "==" and "===", their direct difference is still very big. For "==", it recognizes the empty string, 0 and false are both Null. For "===", only if one variable is really null, it represents null

In addition, "===" has better performance than isset

3. Judgment If a variable is null, just use "==="

4. empty to determine whether the content stored in a variable is zero or empty, 0, "0", null, false, array( ), var $var, and objects without any properties are considered empty and represent zero.

If $a is undefined or the value is NULLL, $a=NULL, it must be empty, that is, empty($a)=true; if $a is of type int, $a=0, it is relative For numbers, 0 represents zero, that is, empty($a)=true;

If $a is of string type, $a="", relative to string, "" represents empty, that is empty($a)=true; If $a is of type string, $a="0", relative to string, "0" means zero, that is, empty($a)=true;

If $a is bool type, $a=false, relative to true, false means empty, that is, empty($a)=true; If $a is array type, $a=array(), relative to array, Data without elements is empty, that is, empty($a)=true;

Recommended learning: "PHP Video Tutorial"

The above is the detailed content of How to determine whether a variable is null in php. For more information, please follow other related articles on the PHP Chinese website!