Storage Classes

Storage Classes in 'C' : 

• Storage classes tells information about storage location for variables, who can access variables, what will be default for it etc. 
• There are four storage classes in 'C' as follow :

1) auto : 

• By default storage class for members is auto. 
• auto keyword is used to declare auto storage class for example auto int age;

• An auto variables are also called as automatic variables. 
• They are stored in a computers memory. 
• Default value for auto variables is unpredictable. 
• They can be accesses inside the function or block.

Amazon prime offers Amazon prime offers

2) register : 

• Variables having register storage class will get stored into a registers in CPU instead of memory. 
• register keyword is used to define register storage class. For example register int age;
• Data from register can be fetched fast as compared to data from memory this is benefit of register storage class. 
• Default value for register varable is any garbage value. 
• They get stored in memory of computer.
• They can be accessed inside a function or block. 

3) extern : 

• It is used to create global data members so that they can be shared among multiple files. 
• extern keyword is used to declare them. For example extern int age=45;
• They can be intialize only once in a original file. 
• Default value of extern variable is zero. 
• They get stored in a memory of computer. 
• They can be accessed in entire file and also in other files where it is declared as extern. 

4) Static : 

• Static keyword is used to declare static storage class for data members in a program. 
• Static members can be both local or global dependinb on way how they are declared. 
• Default value for static variables is zero.  
• Local static members can be access using local scope where as global static members can be access using global scope. 
• They get stored in memory of computer. 
• Important point to note about static variables is they are initialized only once in their lifitime. 
• They persist or retain their values between function call. 
• Example : Consider following code

 #include<stdio.h>

 int main()

{

   int sum()

   {

       //local static var

        Static int sum = 0;

        sum++;

        printf("sum = %d", sum);

    }

  sum();

  sum();

  return 0;

}

Output :

sum = 1

sum = 2

Note : Since static variables persist their value between function calls we get output 1 first function call and 2 for next function call.