Can I Allocate a specific memory address using pointers in c++?

Question

Can I Allocate a specitic memory address using pointers in c++ ?

For example: Allocate This memory address 25D4C3FA and put 4 in it.

Answer 1

Allocating a specific address in your process's address space is a bit tricky and platform-specific. On Unix systems, mmap() is probably the closest you're going to get. The Windows equivalent is VirtualAlloc(). There are, of course, no guarantees since the address might already be in use.

Writing to a specific address is trivial:

char *p = (char*)0x25D4C3FA;
*p = 4;

I assume you have good reasons to want to do that.

Answer 2

In Windows, yes.

pseudo-code:

Pointer desiredAddress = 0xD0000000;

//allocate 1 KB at our desired address
Pointer p = VirtualAlloc(desiredAddress, 1024, 
      MEM_COMMIT | MEM_RESERVE,  
      PAGE_READWRITE);

Answer 3

You can request a specific address through VirtualAlloc on Windows, and I expect other operating systems do the same, but there are no guarantees and no platform-independent means.

Answer 4

Assuming that by allocate you actually mean access,

You can, but if the address is invalid or not accessible then deferencing the address will result in Undefined Behavior.
So it is not a good idea to do so.