Question

Explain different storage classes.

Answer 1

The different locations in the computer where we can store data and their accessibility, initial values etc. vary based on the way they are declared. These different ways are termed as different storage classes. In C, we have four storage classes, namel

1. Automatic
2. Register
3. Static
4. External or Global
   Let us see these storage classes one by one

1. Automatic storage class
   In this case data is stored in memory
   The initial value of such a variable is
   garbage.
   The scope of the variable is local i.e. limited
   to the function in which it is defined.
   The life of such variables is till the control
   remains in the particular function where it is
   defined.
   For e.g.:
   int i; or auto int i;
   In all our programs till now we have been
   using the automatic storage class for our
   variables.

2. Register storage class
   In this case data is stored in CPU register
   The initial value of such a variable is
   garbage.
   The scope of the variable is local i.e. limited
   to the function in which it is defined.
   The life of such variables is till the control
   remains in the particular function where it is
   defined.
   For e.g.:
   register int i;
   In this case the data is stored in a small
   memory inside the processor called as its
   registers.
   The advantage of such storage class is that
   since the data is in the processor itself, its
   access and operations on such data is faster.
   There is a limitation on the size of the data
   that can be declared to be register storage
   class. The data should be such that it doesn’t
   require more than 4 bytes. Hence double and
   long double data types cannot be declared as
   register.
   Also there is a limitation on the maximum
   number of variables in a function that can be
   of register class. The limitation is that a
   maximum of 3 register class variable can be
   declared in a function.

3. Static storage class
   In this case data is stored in memory
   The initial value of such a variable is zero.
   The scope of the variable is local i.e. limited
   to the function in which it is defined.
   The life of such variables is till the program
   is alive.
   For e.g. :
   static int i;
   If a variable is declared static, its value
   remains unchanged even if the function
   execution is completed.