How to store a C++ variable in a register

Question

I would like some clarification regarding a point about the storage of register variables: Is there a way to ensure that if we have declared a register variable in our code,

Answer 1

Generally it's impossibly. Specifically one can take certain measures to increase the probability:

Use proper optimization level eg. -O2

Keep the number of the variables small

register int a,b,c,d,e,f,g,h,i, ... z;  // can also produce an error
// results in _spilling_ a register to stack
// as the CPU runs out of physical registers

Do not take an address of the register variable.

register int a;
int *b = &a;  /* this would be an error in most compilers, but
                 especially in the embedded world the compilers
                 release the restrictions */

In some compilers, you can suggest

register int a asm ("eax");  // to put a variable to a specific register