External ( extern ) storage class in C Programming

January 24, 2010 No Comments » Hits : 230



External ( extern ) storage class in C Programming
  1. Variables of this storage class are “Global variables”
  2. Global Variables are declared outside the function and are accessible to all functions in the program
  3. Generally , External variables are declared again in the function using keyword extern
  4. In order to Explicit declaration of variable use ‘extern’ keyword
extern int num1 ;   // Explicit Declaration
Features :
 StorageMemory
 ScopeGlobal / File Scope
 Life time
  • Exists as long as variable is running
  • Retains value within the function
 Default initial Value
Zero
Live Example : 
int num =  75 ;  

void display();

void main(){ extern int mum ;             printf("nNum : %d",num); display();}

void display(){ extern int mum ;             printf("nNum : %d",num);}
Output :
Num : 75Num : 75
Note :
  1. Declaration within the function indicates that the function uses external variable
  2. Functions belonging to same source code , does not require declaration (no need to write extern)
  3. If variable is defined outside the source code , then declaration using extern keyword is required
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My name is Pritesh Taral. I am working in well known MNC. as Java Developer. I am part time blogger loves writing articles on C/C++. I am active on facebook using community fan page .One can Visit me @ Facebook Facebook Fan Page