src/test/ui/consts/offset_from.rs

   1 // run-pass
   2
   3 #![feature(const_ptr_sub_ptr)]
   4 #![feature(ptr_sub_ptr)]
   5
   6 struct Struct {
   7     field: (),
   8 }
   9
  10 #[repr(C)]
  11 struct Struct2 {
  12     data: u8,
  13     field: u8,
  14 }
  15
  16 pub const OFFSET: usize = {
  17     let uninit = std::mem::MaybeUninit::<Struct>::uninit();
  18     let base_ptr: *const Struct = &uninit as *const _ as *const Struct;
  19     // The following statement is UB (taking the address of an uninitialized field).
  20     // Const eval doesn't detect this right now, but it may stop compiling at some point
  21     // in the future.
  22     let field_ptr = unsafe { &(*base_ptr).field as *const () as *const u8 };
  23     let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
  24     offset as usize
  25 };
  26
  27 pub const OFFSET_2: usize = {
  28     let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
  29     let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
  30     let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
  31     let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
  32     offset as usize
  33 };
  34
  35 pub const OVERFLOW: isize = {
  36     let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
  37     let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
  38     let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
  39     unsafe { (base_ptr as *const u8).offset_from(field_ptr) }
  40 };
  41
  42 pub const OFFSET_EQUAL_INTS: isize = {
  43     let ptr = 1 as *const u8;
  44     unsafe { ptr.offset_from(ptr) }
  45 };
  46
  47 pub const OFFSET_UNSIGNED: usize = {
  48     let a = ['a', 'b', 'c'];
  49     let ptr = a.as_ptr();
  50     unsafe { ptr.add(2).sub_ptr(ptr) }
  51 };
  52
  53 fn main() {
  54     assert_eq!(OFFSET, 0);
  55     assert_eq!(OFFSET_2, 1);
  56     assert_eq!(OVERFLOW, -1);
  57     assert_eq!(OFFSET_EQUAL_INTS, 0);
  58     assert_eq!(OFFSET_UNSIGNED, 2);
  59 }