I have a unsigned const volatile short int*. I want it to be (x + y), which at time of defining is set to 0. However, i want if for some reason y changes to 5, i would want the unsigned const volatile short int* to change too.
Would this be possible in C?
(Note: I am using freestanding C99 mode with GNU extensions, and i mean for it to change automatically and not with a function.)
There is no way to make variables automatically update based on other variables like that in C.
Instead of storing the sum of x and y in a variable, you should consider just making a function that recomputes the sum whenever you need it. The addition should be pretty fast:
int get_the_sum()
{
return x + y;
}
Alternatively, you might consider making x and y be static variables that can only be changed with setter functions. The setter functions for x and y would take care of updating any variables that need to be updated. It's hard to tell whether this approach is worth it without knowing more about your application.
void change_y(int new_y)
{
y = new_y;
sum = x + y;
}
Supposing that y is declared as
volatile unsigned short int y = -x;
(or an equivalent), and that the value of y is initially different from 5, you can define
unsigned const volatile short int *p = &y;
This will satisfy the requirements as you presented them, though it imposes conditions you did not specify. In addition to those explicitly given above, it assumes that the fact that you require changes in response to changes in y, but do not mention changes in response to changes in x means that the pointed-to value in fact does not need to respond to changes in x.
Of course, I'm inclined to think that this doesn't at all represent what you really mean. That cannot be implemented in C. Pointers refer to locations in memory, but the value of an expression such as x + y does not reside in memory.
