search
HomeBackend DevelopmentPHP ProblemWhat is the way to define constants in php
What is the way to define constants in phpFeb 09, 2022 pm 06:53 PM
phpDefine constants

How to define constants in php: 1. Use the define() function to define, the syntax "define (constant name, constant value, whether case sensitive)"; 2. Use the const keyword to define, the syntax "const Constant name = constant value;".

What is the way to define constants in php

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

How to define constants in php

  • define() function

  • const keyword

Compared with variables, Constants have the following characteristics:

  • There is no dollar sign ($) in front of the constant;

  • Constant can only be defined with define() and const ;

  • The scope of constants is global;

  • Once a constant is defined, it cannot be redefined or undefined.

define() function defines constants

Legal constant names can only start with letters and underscores, and can be followed by letters of any length, Numbers or underscores. In PHP, you can define a constant through the define() function. The syntax of the define() function is as follows:

define($name, $value , $case_insensitive)
  • $name Required parameters, constant name (need to use double quotes Or wrapped in single quotes)

  • $value Required parameter, the value of the constant

  • $case_insensitive Optional parameter, specifies whether it is case sensitive, The default is case-sensitive. If set to true, it means that it is not case-sensitive

<?php
header("Content-type:text/html;charset=utf-8");
define(&#39;WebSite&#39;, &#39;php中文网&#39;);
echo WebSite.&#39;<br>&#39;;
?>

What is the way to define constants in php

const keyword definition constant

Syntax:

const 常量名 = 常量值;

Example:

<?php
const FOO = &#39;BAR&#39;;
echo FOO.&#39;<br>&#39;;
?>

What is the way to define constants in php

##The difference between define() and const:

const defines constants at compile time, while the define() method defines constants at runtime.

const cannot be used in if statements, defne() can be used in if statements.

if(...) {
    const FOO = &#39;BAR&#39;;//错误
}
if(...) {
    define(&#39;FOO&#39;, &#39;BAR&#39;);//正确
}

define() A common scenario is to first determine whether the constant has been defined before defining the constant:

if(defined(&#39;FOO)) {
    define(&#39;FOO&#39;, &#39;BAR&#39;)
}

const When defining a constant, the value can only be a static scalar (number, string, true , false, null), and the define() method can use the value of any expression as the value of a constant. Starting from PHP 5.6, const also allows expressions to be used as the value of constants.

const BIT_5 = 1 << 5; //PHP5.6后支持,之前的PHP版本不支持
define(&#39;BIT_5&#39;, 1 << 5);// 所有PHP版本都支持const 只允许简单的常量名,而define()可以把任何表达式的值用作常量名
for ($i = 0; $i < 32; $i++) {
    define(&#39;BIT_&#39; . $i, 1 << $i);
}

const The constant names defined are case-sensitive, and case-insensitive constants can be defined by passing true to the third parameter of the define() method.

define(&#39;FOO&#39;, &#39;BAR&#39;, true);
echo FOO; //BAR
echo foo; //BAR

Listed above are some shortcomings or inflexibility of const compared to define(). Let’s take a look at why I personally recommend using const instead of define() to define constants (unless you need to Define constants in the scenarios listed above).

const has better readability, const is a language structure rather than a function, and is consistent with the form of defining class constants in a class.

const defines constants in the current namespace, and define() must pass the complete namespace name when defining to achieve similar effects:

namespace A\B\C;
//To define the constant A\B\C\FOO:
const FOO = &#39;BAR&#39;;
define(&#39;A\B\C\FOO&#39;, &#39;BAR&#39;);

Recommended learning: "

PHP Video tutorial

The above is the detailed content of What is the way to define constants in php. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
php怎么把负数转为正整数php怎么把负数转为正整数Apr 19, 2022 pm 08:59 PM

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

php怎么实现几秒后执行一个函数php怎么实现几秒后执行一个函数Apr 24, 2022 pm 01:12 PM

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php怎么除以100保留两位小数php怎么除以100保留两位小数Apr 22, 2022 pm 06:23 PM

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

php怎么根据年月日判断是一年的第几天php怎么根据年月日判断是一年的第几天Apr 22, 2022 pm 05:02 PM

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php怎么替换nbsp空格符php怎么替换nbsp空格符Apr 24, 2022 pm 02:55 PM

方法:1、用“str_replace("&nbsp;","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\&nbsp\;||\xc2\xa0)/","其他字符",$str)”语句。

php怎么判断有没有小数点php怎么判断有没有小数点Apr 20, 2022 pm 08:12 PM

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php怎么设置implode没有分隔符php怎么设置implode没有分隔符Apr 18, 2022 pm 05:39 PM

在PHP中,可以利用implode()函数的第一个参数来设置没有分隔符,该函数的第一个参数用于规定数组元素之间放置的内容,默认是空字符串,也可将第一个参数设置为空,语法为“implode(数组)”或者“implode("",数组)”。

php字符串有没有下标php字符串有没有下标Apr 24, 2022 am 11:49 AM

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

SublimeText3 Linux new version

SublimeText3 Linux new version

SublimeText3 Linux latest version

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!