Meaning of *((volatile UINT32*)(a)) in C

Question

What is the meaning of

 *((volatile UINT32*)(a)) ?

in C langauage?

Give me some example.

Answer 1

It dereferences a, after first casting it to type "pointer to volatile UINT32".

There are way more parentheses than needed, it would be better written as:

*(volatile UINT32 *) a

That does the same thing. You'd expect there to be some more code here, of course, either a write:

*(volatile UINT32 *) a = 4711;

that writes 4711 to the address contained in a, making sure (due to the volatile) that the write is not optimized out even if it can seem pointless from the compiler's point of view.

Or a read:

const UINT32 packetCounter = *(volatile UINT32 *) a;

which reads the current value at the address in a, and stores it in a local constant variable called packetCounter. This is how it would look if a is the address of some I/O register. Again due to the volatile, the read must happen, it cannot be optimized out or cached even though it might seem pointless to the compiler. This is common with I/O registers.