Detailed explanation of the meaning and usage of define in php

define() function understanding 1 (focus on understanding the function)

define() 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.

define function understanding 2 (focus on parameter understanding)

Grammar:

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

optional. Specifies whether constant names are case-sensitive.

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

define function understanding 3 (focus on example understanding)

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

## define function understanding 4

Question: 2: A case-insensitive constant:

<?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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