const define difference PHP

When defining constants in PHP, there are two methods: const and define. So what is the difference between them?

1. Const is used to define class member variables. Once defined, its value cannot be changed. define defines global constants and can be accessed anywhere

2. define cannot be defined in a class, but const must be defined in a class, and variables defined by const must be accessed through class name::variable name

3. const cannot define constants in conditional statements

<?php
    if(1){
        const a = &#39;java&#39;;
    }
    echo a;  //必错
?>

4. const uses an ordinary constant name (static scalar), and define can use any expression as the name

<?php
const  FOO = &#39;PHP&#39;; 
for ($i = 0; $i < 32; ++$i) { 
    define(&#39;PHP_&#39; . $i, 1 << $i); 
} 
?>

5. const is always case-sensitive. However, define() can define case-insensitive constants through the third parameter.

6. Using const is simple and easy to read. It itself is A language structure, and define is a method. Using const to define is much faster than define at compile time

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