what does it mean to convert int to void* or vice versa?

Question

What does it mean to convert an integer value to a void* or viceversa from a memory point of view? My understanding is void* is an address to a blo

Answer 1

The C standard specifies that it must be possible to convert a void pointer to an integral type such that converting the integral type back to a void pointer will yield the same pointer. I'm not sure if it requires that converting a null pointer to an integer yield the value zero, or if only numeric literal zeroes are recognized as special. On many implementations, the integer value represents a hardware address, but the standard makes no such guarantee. It would be entirely possible that on hardware which included a special trap for hardware address 0x12345678, converting a pointer to an integer would subtract 0x12345678 from the hardware address, and converting an integer to a pointer would add 0x12345678 back in (thus an integer value of zero would represent a null pointer).

In many cases, particularly when developing for embedded controllers, the compiler vendor will explicitly specify what hardware address will be accessed when converting a particular integer value to a pointer type. On processors with a single linear address space, converting an integer value 0x12345678 to a pointer would generally yield a pointer which refers to address 0x12345678; the hardware reference manual would indicate if there was anything special about that location. On processors with more 'interesting' address spaces, it may be necessary to use something other than the hardware address as the pointer. For example, on antique IBM PC computers, the display buffer was mapped at hardware address 0xB8000, but in most compilers, the address would be expressed as (short far*)0xB8000000.