Types of Storage classes in C language (Part 3)

 Last part of Storage classes 

External storage class:

It is used to declare global variables. These are linked at the time of creating exe file.

 

            Declaration:

           

Syntax :

            extern  int  a;

            extern int a=10; à invalid

           

            extern variable should not be initialized.

 

Program to check scope of the variable.

 

#include<stdio.h>

 

/* below is a global variable but not extern.

    Below variable is global to current file only. It can be accessed from function in the current file.

   If it is external variable, then it is global to all files in the C-Application and it can be accessed at run time from function of any file in C-Application.

*/

 

int a=10;

main()

{

            printf(“ %d “, a);

            f1();

printf(“ %d “, a);

 

            f2();

printf(“ %d “, a);

 

            f1();

printf(“ %d “, a);

 

            f2();

printf(“ %d “, a);

}

 

f1()

{

            int a=10;

            a=a+20;

}

 

f2()

{

 

            a=a+50;

}

 

Global variable as static:

 

#include<stdio.h>

static  int  a=10;

main()

{

            =========;

            =========;

            =========;

}

 

 

If global variables are declared as static, it can not be accessed from the linked files.

main intension of this declaration is to make availability inside the current file only.

 

Extern variable can be accessed from any where in the application, including from linked files.

 

 This part of c language is very much useful and important.