如何检查php中是否存在常量

So im using a php framework called fuelphp, and I have this page that is a html file so i can't use php in it, and I have another file that has a top bar in it, which my html file will call though ajax. And I was just asking, how do we check if a constant exists in php? aka (the fuelphp framework file locations)

我使用一个叫fuelphp的php框架，这个页面是一个html文件，所以我不能在里面使用php，我还有一个文件里面有一个顶栏，我的html文件用ajax调用。我只是问，如何检查php中是否存在常数?aka (fuelphp框架文件位置)

so these are constants I need to check (well I only have to check one of them)

这些是我需要检查的常量(我只需要检查其中一个)

define('DOCROOT', __DIR__.DIRECTORY_SEPARATOR);
    define('APPPATH', realpath(__DIR__.'/fuel/app/').DIRECTORY_SEPARATOR);
    define('PKGPATH', realpath(__DIR__.'/fuel/packages/').DIRECTORY_SEPARATOR);
    define('COREPATH', realpath(__DIR__.'/fuel/core/').DIRECTORY_SEPARATOR);                    
    require APPPATH.'bootstrap.php';

edit:
I realised that these aren't variables they are constants...

编辑:我意识到这些不是变量它们是常量……

6 个解决方案

#1

First, these are not variables, but constants.

首先，这些不是变量，而是常量。

And you can check their existence by using the defined() function :

通过定义()函数可以检验它们的存在性:

bool defined ( string $name )

Checks whether the given constant exists and is defined.

检查给定的常数是否存在和是否定义。

#2

Use defined() function, for example:

使用defined()函数，例如:

if (defined('VAR_NAME')) {
    // Something
}

#3

Check using defined('CONSTANT') function.

检查使用(“常数”)函数定义。

An example from the manual:

手册中的一个例子:

<?php
/* Note the use of quotes, this is important.  This example is checking
 * if the string 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
    echo TEST;
}
?>

#4

here's a cooler & more concise way to do it:

这里有一个更酷更简洁的方法:

defined('CONSTANT') or define('CONSTANT', 'SomeDefaultValue');

credit: daniel at neville dot tk http://php.net/manual/bg/function.defined.php

感谢:daniel在neville dot tk http://php.net/manual/bg/function.definedphp

#5

I take it you mean CONSTANTS not variables! the function is defined();

我猜你是说常数而不是变量!定义的函数();

see here: defined

在这里看到的:定义

#6

i use this method:

我用这个方法:

if (defined('My_variable') && (DEFAULT_LANGUAGE != '') && (DEFAULT_LANGUAGE != 'My_variable') )
{
  // your codes here
}

#1