Define External Storage Class - computer programming?

When a variable is declared outside a function the storage is permanently assigned to it and its storage class is 'extern' and a declaration for an external variable can look just the name as a local variable declaration. Such a variable is considered to be as global to all functions declared later than and upon exit from the function or block, the external variable remains in existence. These variables are able to be accessed by any function in the program.

Illustration is

extern int a=1, b=2;

The External variables never disappear because they exist throughout the execution life of the program and they can be used to transmit value across functions. They may be unseen if the identifier is redefined.

All the functions have external storage class. This signifies that the key word extern can be used in function prototypes and in function definitions.