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Per page move: Changed link from Class (computer programming) to Class (programming) using MovePlus

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	In [[object-oriented programming]], a '''member variable''' (sometimes called a '''member [[Field (computer science)\|field]]''') is a [[variable (programming)\|variable]] that is associated with a specific [[Object (computer science)\|object]], and accessible for all its [[method (computer science)\|methods]] (''member functions'').		In [[object-oriented programming]], a '''member variable''' (sometimes called a '''member [[Field (computer science)\|field]]''') is a [[variable (programming)\|variable]] that is associated with a specific [[Object (computer science)\|object]], and accessible for all its [[method (computer science)\|methods]] (''member functions'').

	In [[class-based programming]] languages, these are distinguished into two types: ''[[class variable]]s'' (also called ''static member variables''), where only one copy of the variable is shared with all [[instance (computer science)\|instance]]s of the [[Class (~~computer~~ programming)\|class]]; and ''[[instance variable]]s'', where each instance of the class has its own independent copy of the variable.<ref>{{cite web \| accessdate = 2011-08-12 \| author = Richard G. Baldwin \| date = 1999-03-10 \| publisher = Richard G Baldwin Programming Tutorials \| title = Q - What is a member variable? \| quote = A member variable is a member of a class (class variable) or a member of an object instantiated from that class (instance variable). It must be declared within a class, but not within the body of a method of the class. \| url = http://www.dickbaldwin.com/java/Java020.htm}}</ref>		In [[class-based programming]] languages, these are distinguished into two types: ''[[class variable]]s'' (also called ''static member variables''), where only one copy of the variable is shared with all [[instance (computer science)\|instance]]s of the [[Class (programming)\|class]]; and ''[[instance variable]]s'', where each instance of the class has its own independent copy of the variable.<ref>{{cite web \| accessdate = 2011-08-12 \| author = Richard G. Baldwin \| date = 1999-03-10 \| publisher = Richard G Baldwin Programming Tutorials \| title = Q - What is a member variable? \| quote = A member variable is a member of a class (class variable) or a member of an object instantiated from that class (instance variable). It must be declared within a class, but not within the body of a method of the class. \| url = http://www.dickbaldwin.com/java/Java020.htm}}</ref>

	== Examples ==		== Examples ==

imported>Zaelzo: change title of examples section from "For Examples" to "Examples"

2025-01-13T05:04:31Z

change title of examples section from "For Examples" to "Examples"

New page

{{Short description|Variable associated with a specific object, and accessible for all its methods}}
In [[object-oriented programming]], a '''member variable''' (sometimes called a '''member [[Field (computer science)|field]]''') is a [[variable (programming)|variable]] that is associated with a specific [[Object (computer science)|object]], and accessible for all its [[method (computer science)|methods]] (''member functions'').

In [[class-based programming]] languages, these are distinguished into two types: ''[[class variable]]s'' (also called ''static member variables''), where only one copy of the variable is shared with all [[instance (computer science)|instance]]s of the [[Class (computer programming)|class]]; and ''[[instance variable]]s'', where each instance of the class has its own independent copy of the variable.<ref>{{cite web | accessdate = 2011-08-12 | author = Richard G. Baldwin | date = 1999-03-10 | publisher = Richard G Baldwin Programming Tutorials | title = Q - What is a member variable? | quote = A member variable is a member of a class (class variable) or a member of an object instantiated from that class (instance variable). It must be declared within a class, but not within the body of a method of the class. | url = http://www.dickbaldwin.com/java/Java020.htm}}</ref>

== Examples ==
=== C++ ===
<syntaxhighlight lang="cpp">

class Foo {
int bar; // Member variable
public:
void setBar(const int newBar) {
bar = newBar;
}
};

int main () {
Foo rect; // Local variable

return 0;
}</syntaxhighlight>

=== Java ===
<syntaxhighlight lang="java">
public class Program
{
public static void main(String[] args)
{
// This is a local variable. Its lifespan
// is determined by lexical scope.
Foo foo;
}
}

public class Foo
{
/* This is a member variable - a new instance
of this variable will be created for each
new instance of Foo. The lifespan of this
variable is equal to the lifespan of "this"
instance of Foo
*/

int bar;
}
</syntaxhighlight>

=== Python ===
<syntaxhighlight lang="python">
class Foo:
def __init__(self):
self._bar = 0

@property
def bar(self):
return self._bar

@bar.setter
def bar(self, new_bar):
self._bar = new_bar

f = Foo()
f.bar = 100
print(f.bar)
</syntaxhighlight>

=== Common Lisp ===
<syntaxhighlight lang="lisp">
(defclass foo () (bar))

(defvar f (make-instance 'foo))
(setf (slot-value f 'bar) 100)
(print (slot-value f 'bar))
</syntaxhighlight>

=== Ruby ===
<syntaxhighlight lang="ruby">
/*
Ruby has three member variable types: class, class instance, and instance.
*/

class Dog

# The class variable is defined within the class body with two at-signs
# and describes data about all Dogs *and* their derived Dog breeds (if any)
@@sniffs = true

end

mutt = Dog.new
mutt.class.sniffs #=> true

class Poodle < Dog

# The "class instance variable" is defined within the class body with a single at-sign
# and describes data about only the Poodle class. It makes no claim about its parent class
# or any possible subclass derived from Poodle
@sheds = false

# When a new Poodle instance is created, by default it is untrained. The 'trained' variable
# is local to the initialize method and is used to set the instance variable @trained
# An instance variable is defined within an instance method and is a member of the Poodle instance
def initialize(trained = false)
@trained = trained
end

def has_manners?
@trained
end

end

p = Poodle.new
p.class.sheds #=> false
p.has_manners? #=> false
</syntaxhighlight>

=== PHP ===
<syntaxhighlight lang="php">
<?php

class Example
{
/**
* Example instance member variable.
*
* Member variables may be public, protected or private.
*
* @var int
*/
public int $foo;

/**
* Example static member variable.
*
* @var bool
*/
protected static int $bar;

/**
* Example constructor method.
*
* @param int $foo
*/
public function __construct(int $foo)
{
// Sets foo.
$this->foo = $foo;
}
}

// Create a new Example object.
// Set the "foo" member variable to 5.
$example = new Example(5);

// Overwrite the "foo" member variable to 10.
$example->foo = 10;

// Prints 10.
echo $example->foo;
</syntaxhighlight>

=== Lua ===
<syntaxhighlight lang="lua">
--region example
--- @class example_c
--- @field foo number Example "member variable".
local example_c = {}
local example_mt = {__index = example_c}

--- Creates an object from example.
--- @return example_c
function example_c.new(foo)
-- The first table argument is our object's member variables.
-- In a Lua object is a metatable and its member variables are table key-value pairs.
return setmetatable({
foo = foo
}, example_mt)
end
--endregion

-- Create an example object.
-- Set the "foo" member variable to 5.
local example = example_c.new(5)

-- Overwrite the "foo" member variable to 10.
example.foo = 10

-- Prints 10.
print(example.foo)
</syntaxhighlight>

== See also ==
* [[Global variable]]
* [[Local variable]]
* [[Property (programming)]]

== References ==
{{Reflist}}

[[Category:Object-oriented programming]]
[[Category:Variable (computer science)]]
[[Category:Articles with example Python (programming language) code]]

Member variable - Revision history

imported>TarnishedPath: Per page move: Changed link from Class (computer programming) to Class (programming) using MovePlus

imported>Zaelzo: change title of examples section from "For Examples" to "Examples"