What is an extern storage class in C language?

There are four storage classes in C programming language, which are as follows −

• auto
• extern
• static
• register

Global variables / External variables

The keyword is extern. These variables are declared outside the block.

• Scope − Scope of a global variable is available throughout the program.

• Default value is zero.

Algorithm

The algorithm is given below −

START
Step 1: Declare and initialized extern variable
Step 2: Declare and initialized int variable a=3
Step 3: Print a
Step 4: Call function step 5
Step 5: Called function
Print a (takes the value of extern variable)

Example

Following is the C program for extern storage class −

extern int a =5; /* this ‘a’ is available entire program */
main ( ){
   int a = 3; /* this ‘a' is valid only in main */
   printf ("%d",a);
   fun ( );
}
fun ( ){
   printf ("%d", a);
}

Output

The output is stated below −

3 1

Consider another program for extern storage class −

Example

External.h
extern int a=14;
extern int b=8;
externstorage.c file
#include<stdio.h>
#include "External.h"
int main(){
   int sub = a-b;
   printf("%d -%d = %d ", a, b, sub);
   return 0;
}

Output

The output is stated below −

a-b=6