Detailed explanation of the use of define() and defined() functions in php

In the previous article, we introduced the use of define() in php, and the difference between define() and const in php. Today we will continue to introduce the define() function and defined() function in php. The usage is analyzed and introduced in detail, please refer to it if you need it!

The define() function defines a constant.
The define() function defines a constant.
Constants are much like variables, except for the following differences:
Constant [constant] has many similarities with variables [variable], so it is easy to confuse; below, we list the constants [constant] The difference between ] and variable [variable]:

•A constant's value cannot be changed after it is set
A constant value cannot be changed after it is specified;
•Constant names do not need a leading dollar sign ($)
When setting constants, there is no need to add the "$" sign in front;
•Constants can be accessed regardless of scope
Constant values ​​can only be strings and numbers
Constant values ​​can only be strings and numbers String
[string]" and "number[number]";
Syntax

Syntax
The code is as follows:

define(name,value,case_insensitive)

ParameterParameternamed. Specifies the name of the constantvalueRequired. Specifies the value of the constantcase_insensitiveOptional. Specifies whether the constant name should be case-insensitive. If set to TRUE, the constant will be case-insensitive. Default is FALSE (case-sensitive)

Description Description
Require	Required parameters. Specifies the name of the constant
Required parameter. Specifies the value of the constant
Optional parameters. Specifies whether the name of the constant is case-insensitive. If set to True, letters are not case-sensitive; if set to False, letters are case-sensitive. The default value is: False

Example 1Case 1

Define a case-sensitive constant:

Specify a constant (case sensitive):

The code is as follows:

<?phpdefine("GREETING","Hello you! How are you today?");echo constant("GREETING");?>

The output of the code above will be:

The above code will output the following results:

Hello you! How are you today?

Example 2

Case 2
Define a case-insensitive constant:Specify a constant (case-insensitive):

<?phpdefine("GREETING","Hello you! How are you today?",TRUE);echo constant("greeting");?>

The output of the code above will be:
The above code will output the following results:

Hello you! How are you today?

The defined() function checks whether a constant exists.
defined() The function is to check whether a constant exists.

Returns TRUE if the constant exists, or FALSE otherwise.
If the constant exists, it returns True; if it does not exist, it returns False.

Syntax
Syntax

defined(name)

ParameterParameternameRequired. Specifies the name of the constant to check object

Example
案例

<?phpdefine("GREETING","Hello you! How are you today?");echo defined("GREETING");?>

The output of the code above will be:
上述代码将输出下面的结果：

1

总结：

本文通过示例讲述了php中define()与defined()函数的使用详解，希望对你的工作上有所帮助！

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php常量define与const的区别详解

php中define的使用详解

php define常量定义与变量区别_PHP教程

Description Description
Required parameters. Specify the name of the constant

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