STORAGE CLASS

A storage class defines the scope & life time of variables &/or functions within a c program.

There are four storage classes in c.

• Automatic storage class(keyword-auto)
  
• Register storage class(keyword-register)
  
• Static storage class(keyword- static)
  
• External storage class(keyword-extern)
  

  Note:-
  

  (1-)
  Automatic, Static, External storage classes are having same
  

  Storage- Memory while Register storage class has storage-CPU Register.
  

  (2-)Automatic & Register storage classes are having same
  

  Default initial value-Garbage value whereas Static & External storage class are having same Default initial value- zero.
  

  (3-)
  Automatic, Register & Static storage classes are having same
  

  Scope-Local to the block in which the variable is defined while External storage class has Scope- Global.
  

  (4-) Automatic & Register storage class are having same Life- Till the control remains within the block in which the variable is defined whereas Static storage class has Life-Value of the variable persists between different function calls
  & External storage class has Life-AS long as the program's execution doesn't come to an end.
  

  
   

Features of a variable	Automatic storage class	Register storage class	Static storage class	External storage class
Storage	memory	CPU Register	memory	memory
Default initial value	Garbage value	Garbage value	zero	zero
Scope	Local to the block in which the variable is defined	Local to the block in which the variable is defined	Local to the block in which the variable is defined	Global
Life	Till the control remains within the block in which the variable is defined	Till the control remains within the block in which the variable is defined	Value of the variable persists between different function calls	As long as the program's execution doesn't come to an end
Keywords	auto	register	static	extern