php php中的全局变量没有按预期工作
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global variables in php not working as expected
提问by Josh Smeaton
I'm having trouble with global variables in php. I have a $screenvar set in one file, which requires another file that calls an initSession()defined in yet another file. The initSession()declares global $screenand then processes $screen further down using the value set in the very first script.
我在 php 中遇到全局变量的问题。我$screen在一个文件中设置了一个 var，它需要另一个调用另一个文件中initSession()定义的文件。该initSession()声明global $screen，然后进一步处理$屏幕下使用非常的第一个脚本设置的值。
How is this possible?
这怎么可能？
To make things more confusing, if you try to set $screen again then call the initSession(), it uses the value first used once again. The following code will describe the process. Could someone have a go at explaining this?
更令人困惑的是，如果您尝试再次设置 $screen 然后调用initSession()，它将再次使用第一次使用的值。下面的代码将描述这个过程。有人可以解释一下吗？
$screen = "list1.inc"; // From model.php
require "controller.php"; // From model.php
initSession(); // From controller.php
global $screen; // From Include.Session.inc
echo $screen; // prints "list1.inc" // From anywhere
$screen = "delete1.inc"; // From model2.php
require "controller2.php"
initSession();
global $screen;
echo $screen; // prints "list1.inc"
Update:
If I declare $screenglobal again just before requiring the second model, $screen is updated properly for the initSession()method. Strange.
更新：
如果我$screen在需要第二个模型之前再次声明global ，则 $screen 会为该initSession()方法正确更新。奇怪的。
回答by e-satis
GlobalDOES NOT make the variable global. I know it's tricky :-)
Global不会使变量成为全局变量。我知道这很棘手:-)
Globalsays that a local variable will be used as if it was a variable with a higher scope.
Global表示将使用局部变量，就好像它是具有更高范围的变量一样。
E.G :
EG :
<?php
$var = "test"; // this is accessible in all the rest of the code, even an included one
function foo2()
{
global $var;
echo $var; // this print "test"
$var = 'test2';
}
global $var; // this is totally useless, unless this file is included inside a class or function
function foo()
{
echo $var; // this print nothing, you are using a local var
$var = 'test3';
}
foo();
foo2();
echo $var; // this will print 'test2'
?>
Note that global vars are rarely a good idea. You can code 99.99999% of the time without them and your code is much easier to maintain if you don't have fuzzy scopes. Avoid globalif you can.
请注意，全局变量很少是一个好主意。如果没有模糊范围，您可以在 99.99999% 的时间内编写代码，并且您的代码更容易维护。global如果可以，请避免。
回答by Athena
global $foodoesn't mean "make this variable global, so that everyone can use it". global $foomeans "within the scope of this function, use the global variable $foo".
global $foo并不意味着“将此变量设为全局变量，以便每个人都可以使用它”。global $foo意思是“在这个函数的范围内，使用全局变量$foo”。
I am assuming from your example that each time, you are referring to $screen from within a function. If so you will need to use global $screenin each function.
我从你的例子中假设每次，你都是从一个函数中引用 $screen 。如果是这样，您将需要global $screen在每个函数中使用。
回答by Internet Friend
If you have a lot of variables you want to access during a task which uses many functions, consider making a 'context' object to hold the stuff:
如果在使用许多函数的任务期间要访问很多变量，请考虑创建一个“上下文”对象来保存这些内容：
//We're doing "foo", and we need importantString and relevantObject to do it
$fooContext = new StdClass(); //StdClass is an empty class
$fooContext->importantString = "a very important string";
$fooContext->relevantObject = new RelevantObject();
doFoo($fooContext);
Now just pass this object as a parameter to all the functions. You won't need global variables, and your function signatures stay clean. It's also easy to later replace the empty StdClass with a class that actually has relevant methods in it.
现在只需将此对象作为参数传递给所有函数。您不需要全局变量，并且您的函数签名保持干净。稍后将空的 StdClass 替换为实际包含相关方法的类也很容易。
回答by finnw
You need to put "global $screen" in every function that references it, not just at the top of each file.
您需要在引用它的每个函数中放置“全局 $screen”，而不仅仅是在每个文件的顶部。
回答by zobier
The global scope spans included and required files, you don't need to use the global keyword unless using the variable from within a function. You could try using the $GLOBALS array instead.
全局范围跨越包含文件和必需文件，除非在函数内使用变量，否则不需要使用 global 关键字。您可以尝试改用 $GLOBALS 数组。
回答by Brynner Ferreira
You must declare a variable as global before define values for it.
您必须先将变量声明为全局变量，然后才能为其定义值。
回答by user3651145
It is useless till it is in the function or a class. Global means that you can use a variable in any part of program. So if the global is not contained in the function or a class there is no use of using Global
除非它在函数或类中，否则它是无用的。全局意味着您可以在程序的任何部分使用变量。因此，如果全局不包含在函数或类中，则没有使用 Global
