What are the uses of define in php

Usage of define in php: 1. [define()] function defines a constant; 2. Define the constant name and value, the code is [define(name, value, case_insensitive)]; 3. Define a size Write sensitive constants.

Usage of define in php:

1. Understanding the define() function 1

define()The function defines a constant.

Characteristics of constants:

Constants are similar to variables. The difference is: after setting, the value of the constant cannot be changed. The constant name does not need the dollar sign ($) at the beginning. The scope Does not affect access to constants, constant values ​​can only be strings or numbers.

2. Define function understanding 2

Syntax

define(name,value,case_insensitive)

Parameter description

• name is required. Specifies the name of the constant. //The name parameter is the first parameter of the define function and is in uppercase;

• value is required. Specifies the value of the constant. //The value of value is generally a string or number

• case_insensitive is optional. Specifies whether constant names are case-sensitive.

• If set to true, it will not be case sensitive. Default is false (case sensitive).

3. Define function understanding 3

Question 1: A case-sensitive constant:

<?php
define("HF","Hi Friend!");//1.define函数如何理解；
echo constant("HF");//1.case_insensitive参数默认是 false（大小写敏感）2.constant函数如何理解； 3.constant内的参数如何理解；
 ?>

The output result is :

Hi Friend!

Note: Enter the symbols accurately, otherwise it is easy to make mistakes;

4. Understanding the define function 4

Question: 2: One upper and lower case is not correct Sensitive constants:

<?php 
define("HF","Hi Friend!",TRUE);//1.define函数如何理解； 2.define内的3个参数如何理解；
echo constant("hf"); //1.echo函数如何理解；2.constant函数如何理解； 3.constant函数输入时是否可以不区分大小写； 4.constant函数内的参数如何理解；
?>

The output result is:

Hi Friend!

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