pointer to a structure

[studentc]

given the code

struct DISK_REGISTER {
unsigned ready:1;
unsigned error_occured:1;
unsigned disk_spinning:1;
unsigned write_protect:1;
unsigned head_loaded:1;
unsigned error_code:8;
unsigned track:9;
unsigned sector:5;
unsigned command:5;
}

can i have

struct DISK_REGISTER *disk_reg = &DISK_REGISTER_MEMORY;

on the link
gd.tuwien.ac.at/languages/c/programming-dmarshall/node13.html

instead of the second piece of code, we have

struct DISK_REGISTER *disk_reg = (struct DISK_REGISTER *)DISK_REGISTER_MEMORY;

[quzah]

Well that's wrong. If "DISK_REGISTER_MEMORY" is a single instance of a structure, you can't just tell it that that instance is a pointer and expect it to work right. It doesn't work like that. Otherwise, you could do:

int x, *ptr;

ptr = (int *)x;

Which is clearly not correct. So, the answer is, if "DISK_REGISTER_MEMORY" is an instance of your structure, then your assignment you want to make would be correct. However, I didn't go to your link, so unless someone else feels like doing it...

Quzah.

[studentc]

you mean my code is right
and dmasrahll's code is wrong??

[quzah]

There's no way to say. Looking at the link, there is no place on it where they actually define "DISK_REGISTER_MEMORY", so there is no way of knowing what it is supposed to represent. You can't just say:

To access values stored at a particular memory address, DISK_REGISTER_MEMORY we can assign a pointer of the above structure to access the memory via:

struct DISK_REGISTER *disk_reg = (struct DISK_REGISTER *) DISK_REGISTER_MEMORY;

And expect to be able to decypher what it is they're talking about. They never state what exactly "DISK_REGISTER_MEMORY" is. They should have defined it some place. I assume they're trying to say that "DISK_REGISTER_MEMORY" is a physical instance. I suppose what they meant to say is "If we have an instance of our DISK_REGISTER structure, called "DISK_REGISTER_MEMORY", then we can do...

struct DISK_REGISTER DISK_REGISTER_MEMORY;
struct DISK_REGISTER *disk_reg;

disk_reg = &DISK_REGISTER_MEMORY;

In which case, they're correct. However, it's poorly worded. If that is in fact what they mean, then no, you can't do what you want to do.

Quzah.

[studentc]

thanks dude
what you says makes sense.