Storage Classes in C

In C language, four types of storage classes are used to store the variables in the RAM or CPU memory register.

• auto storage class
• static storage class
• register storage class
• extern storage class

auto storage class:

It is the default storage class, it is used to declare variables with the keyword auto.
Example :

void main()
{
void test(void);
auto int x;
{
auto int x=20;
printf("Value of x in inner block is %d",x);
}
test();
printf("Value of x in outer block is %d",x);
}
void test(void);
{
auto int x=25;
printf("Value of x in functional block is %d", x);
}

static storage class:

Static variables are active in the block in which they are declared and they retain the new value, it is also used to declare variables with the keyword static.

Example :

void main(){
void test(void);
printf("First functional call");
test();
printf("Second functional call");
test();
}
void test()
{
static int x=10, y=20;
x=x+10;
y=y+10;
printf("Value of x is : %d and y is : %d",x,y);
}

register storage class:

Variables declared using this class are stored in the CPU memory register, it is used to declare variables with the keyword register. Only a few variables are used in the program declared by using this class to improve the program execution speed.

Example:

void main()
{
register int x=10;
register char sk='Hello';
printf("Value of x is : %d",x);
printf("Value of choice sk is : %c",sk);
}

extern storage class:

Extern class is used to consider a local variable in a block as a global variable, it is used to declare variables with the keyword extern.

Example :

void main()
{
extern int x,y;
void test();
x=10;
y=20;
test();
printf("Value of x is : %d and y is : %d",x,y);
}
void test()
{
extern int x,y;
printf("Value of x is : %d and y is : %d",x,y);
x=x+10;
y=y+10;
}