PHP Function scopes. Trouble coping up with $this vs. global declaration [duplicate] - php

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Closed 10 years ago.
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Access global variable from within a class
I want to fortify my knowledge in PHP. But most of the time I have trouble understanding with scopes. I am not sure when to use $this and global declaration keyword on my functions.
This is just an example class I just omitted the __construct()
class myClass{
public myVariable;
public function1() {
$this->myVariable=1;
}
public function2(){
global $myVariable;
$myVariable=1;
}
}
Which one is the best approach to use when assigning pre-declared variables inside a function? I am confused somehow by the different books by major publishers in PHP. I am not sure if I am asking the correct question or somehow relevant.

Answer 1

First off, thats not valid PHP, as Jared Farrish already said. Its public $myvar instead of public myvar. Variable names always begin with $.
When you declare a variable in a class:
<?php
class A
{
private $var;
}
That variable will be automatically available in all methods if accessed through $this (unless the method static, but that is another story). So this would work:
<?php
class A
{
private $var;
public function foo () {
// This works
$this->var = 1;
// This is a completely different thing and does not change
// the contents of A::$var
$var = 1;
}
}
Now global is a different thing altogether. In PHP, you cant do this:
<?php
$global_a = 123;
function myfunc ()
{
// You wont actually change the value of $global_a with this
$global_a = 1234;
}
echo $global_a; // still 123
You'd think this would work, but global variables aren't automatically available to functions. This is where global comes in:
<?php
$global_a = 123;
function myfunc ()
{
global $global_a;
$global_a = 1234;
}
echo $global_a; // now it will be 1234
I suggest you read about variable scope in PHP and then you can go on to OOP in PHP.
PHP is a very quirky language. Just because something works in most languages in a certain way doesn't mean it will work in PHP. Most of the times, it wont. So its best to educate yourself as much as possible.
Hope this helps

Answer 2

Which one is best often depends on the situation. In general it's best to avoid global variables as they bring risks with them of not knowing exactly where they're used.
Using a class variable is a good option if the variable is specific to that instance of the class. (You will have to prefix it with a $, though. I.e., public $myVariable;).
If the variable is only relevant to the function and instances outside the class, you'd do best to pass it as an reference. This is done by adding an & before the $ in the parameter space. I.e.:
public function3(&$myVariable) {
$myVariable = 1;
}
Or alternatively just return the value you wish and set it outside the function. I.e.,:
class MyClass {
public function3() {
return 1;
}
}
$myObject = new MyClass();
$myVariable = $myObject->function4();

Answer 3

try to avoid passing global variable,as there are many good reasons for that:
Reusing parts of the script is impossible :
If a certain function relies on global variables, it becomes almost impossible to use that function in a different context. Another problem is that you can’t take that function, and use it in another script.
Solving bugs is much harder :
Tracking a global variable is much harder than a non-global variable.
Understanding the code in a year will be much more difficult :
Globals make it difficult to see where a variable is coming from and what it does.
Now your questions:
Which one is the best approach to use when assigning pre-declared variables inside a function?
You can pass them by value or reference inside a function
By value
$firstVar = 1;
function abc($firstVar){
echo $firstVar ; // will give you 1
}
By reference
function abc(&$firstVar){
$firstVar = 3; // this will give utility to change that variable even
echo $firstVar ; // will give you 3
}
Now where to use $this variable:
$this is used to refer to the current object.
example:
class abc{
private $firstVar;
function abc(){
$this->firstVar = 2;
}
}