The different locations in the computer where we can store data and their
accessibility, initial values etc. very based on the way they are declared. These
different ways are termed as different storage classes.
• In C there are for storage classes, namely
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;
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 its
registers.
The advantage of such storage class is that since the data is in the processor itself,
its access and operation on such data is faster.
There is limitation on the size of the data that can 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 a register.
Also there is a limitation on the maximum number of variables in a function that
can be a 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 a memory
MUQuestionPapers.com 13
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 variable 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.
When the execution to that function returns, the previous value is retained.
Thus it says the initialization is only once. If you have an initialization statement of a
static member, it will be executed only once i.e. for the first time when this
function is called.
4. External or global 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 global i.e. it is accessible from anywhere in the
program.
The life such a variable is till the program is alive.
