Register storage classes.
The keyword “register” is used to declare a variable of the register storage class.
Example:
register int a;
A register storage class variable is stored in CPU registers.
Properties
| Storage | CPU register. |
| Default initial value | Garbage value. |
| Scope | Local to the block in which the variables is defined. |
| Life | Till the control remains within the block in which the variable is defined. |
Example:1
#include<stdio.h>
int main()
{
register int i;
for(i=1;i<=100;i++)
printf("\n%d",i);
return(0);
}
Note: A variable stored in a CPU register can always be accessed faster than the one which is stored in memory.
Therefore if we want to access a variable again and again then it is better to declare the variable of the register storage class.
We cannot use the register storage class for all types of variables. For example, the following declarations are wrong:
register float q;
register double a;
register long c;
This is because the CPU registers in a microcomputer are usually 16-bit registers and therefore cannot hold a float value or a double value, which requires 4 and 8 bytes respectively for storing a value.
However, if you use the above declarations you won’t get any error messages.
In such cases, the compiler would treat the variables to be of automatic storage class.
