Comparison storage classes

In C, storage class provides information about their location and visibility.
C provides four storage classes as:

1. auto storage class
2. register storage
3. extern storage class
4. static storage class

• Storage class determines its storage duration, scope and linkage.
• Storage duration is the period during which that identifier exists in the memory.
• Scope is where the identifier can be referenced in a program.
• Linkage determines for a multiple-source file.

Let's summarised all storage classes in C as following as:

Features	Automatic Storage Class	Register Storage Class	Static Storage Class	External Storage Class
Keyword	auto	register	static	extern
Initial Value	Garbage	Garbage	Zero	Zero
Storage	Memory	CPU register	Memory	Memory
Scope	scope limited,local to block	scope limited,local to block	scope limited,local to block	Global
Life	limited life of block,where defined	limited life of block,where defined	value of variable persist between different function calls	Global,till the program execution
Memory location	Stack	Register memory	Segment	Segment
Example	void main() {   auto int i;   printf("%d",i); } OUTPUT 124	void main() {   register int i;   for(i=1; i<=5 ; i++);     printf("%d ",i); } OUTPUT 1 2 3 4 5	void add(); void main() {   add();   add(); } void add() {   static int i=1;   printf("\n%d",i);   i=i+1; } OUTPUT 1 2	void main() {   extern int i;   printf("%d",i);   int i=5 } OUTPUT 5

FIGURE: Table of Storage classes in C

You might also like to read:

1. What is storage classes in C
2. Automatic storage class
3. Register  storage class
4. Static  storage class
5. External  storage class