Member variable

In object-oriented programming, a member variable (sometimes called a member field) is a variable that is associated with a specific object, and accessible for all its methods (member functions). In class-based languages, these are distinguished into two types: if there is only one copy of the variable shared with all instances of the class, it is called a class variable or static member variable; while if each instance of the class has its own copy of the variable, the variable is called an instance variable.[1]

Examples

C++

 1 class Foo {
 2     int bar; // Member variable
 3   public:
 4     void setBar(const int newBar) { 
 5       bar = newBar;
 6     }
 7 };
 8 
 9 int main () {
10   Foo rect; // Local variable
11 
12   return 0;
13 }

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;
}

Python

class Foo:

  @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)

See also

References

  1. ↑ Richard G. Baldwin (1999-03-10). "Q - What is a member variable?". http://www.dickbaldwin.com/: Richard G Baldwin Programming Tutorials. Retrieved 2011-08-12. 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.
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