What is the difference between auto storage class and register storage class?

Answer 1

register behaves like auto class but auto variables are actually local variables.They are created when the functions are created but they are destroyed when the fns is exited.But register-variables are used to speed up the operations

Answer 2

keyword register can be used for parameters and local variables, it means two things:

- it is often used variable (parameter), so the compiler might want to use a CPU-register to optimize its using.

- the programmer swears that he won't ever use the address of that variable (parameter)

example:

size_t strlen (register const char *s)

{

register const char *q= s-1;

while (*++q);

return q-s;

}