Is the address of a variable in C the real address in the RAM of the computer?

Question

In C, when you get the address of a variable is that address an address that really exist in the RAM of the computer or just an address in a fake memory in the C compiler (if that's how it really works)? Can you explain in layman’s terms?

Answer 1

Yes and no. When you take the address of a variable, and perform some operations on it (assuming the compiler doesn't optimize it out), it will correspond to an address in ram. However because of virtual memory, the address used in your program is almost certainly not the address of the variable in physical ram. The kernel remaps what virtual addresses (what your program sees) refer to which physical addresses (what the memory sees), so that different processes can be loaded into memory at the same time, yet not be able to access each others' memory. Additionally, your process's memory can be paged out, or written to disk if it has not been used recently and/or something else needs more memory, and reloaded into a completely different address, yet the virtual address will remain the same.

So yes, when you access a pointer, that address corresponds to an address in memory. But that address doesn't correspond to the actual address in ram, and the address it corresponds to can change over time.