diff options
| -rw-r--r-- | library/core/src/ptr/const_ptr.rs | 22 | ||||
| -rw-r--r-- | library/core/src/ptr/mut_ptr.rs | 22 |
2 files changed, 44 insertions, 0 deletions
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs index 7d7306574a6..82b52b9aaf2 100644 --- a/library/core/src/ptr/const_ptr.rs +++ b/library/core/src/ptr/const_ptr.rs @@ -303,6 +303,9 @@ impl<T: ?Sized> *const T { /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// + /// * Both pointers must be *derived from* a pointer to the same object. + /// (See below for an example.) + /// /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. /// /// * The distance between the pointers, in bytes, must be an exact multiple @@ -348,6 +351,25 @@ impl<T: ?Sized> *const T { /// assert_eq!(ptr2.offset(-2), ptr1); /// } /// ``` + /// + /// *Incorrect* usage: + /// + /// ```rust,no_run + /// #![feature(ptr_offset_from)] + /// + /// let ptr1 = Box::into_raw(Box::new(0u8)) as *const u8; + /// let ptr2 = Box::into_raw(Box::new(1u8)) as *const u8; + /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize); + /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1. + /// let ptr2_other = (ptr1 as *const u8).wrapping_offset(diff); + /// assert_eq!(ptr2 as usize, ptr2_other as usize); + /// // Since ptr2_other and ptr2 are derived from pointers to different objects, + /// // computing their offset is undefined behavior, even though + /// // they point to the same address! + /// unsafe { + /// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior + /// } + /// ``` #[unstable(feature = "ptr_offset_from", issue = "41079")] #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")] #[inline] diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs index 3daeec36041..aa9619755ac 100644 --- a/library/core/src/ptr/mut_ptr.rs +++ b/library/core/src/ptr/mut_ptr.rs @@ -474,6 +474,9 @@ impl<T: ?Sized> *mut T { /// byte past the end of the same allocated object. Note that in Rust, /// every (stack-allocated) variable is considered a separate allocated object. /// + /// * Both pointers must be *derived from* a pointer to the same object. + /// (See below for an example.) + /// /// * The distance between the pointers, **in bytes**, cannot overflow an `isize`. /// /// * The distance between the pointers, in bytes, must be an exact multiple @@ -519,6 +522,25 @@ impl<T: ?Sized> *mut T { /// assert_eq!(ptr2.offset(-2), ptr1); /// } /// ``` + /// + /// *Incorrect* usage: + /// + /// ```rust,no_run + /// #![feature(ptr_offset_from)] + /// + /// let ptr1 = Box::into_raw(Box::new(0u8)); + /// let ptr2 = Box::into_raw(Box::new(1u8)); + /// let diff = (ptr2 as isize).wrapping_sub(ptr1 as isize); + /// // Make ptr2_other an "alias" of ptr2, but derived from ptr1. + /// let ptr2_other = (ptr1 as *mut u8).wrapping_offset(diff); + /// assert_eq!(ptr2 as usize, ptr2_other as usize); + /// // Since ptr2_other and ptr2 are derived from pointers to different objects, + /// // computing their offset is undefined behavior, even though + /// // they point to the same address! + /// unsafe { + /// let zero = ptr2_other.offset_from(ptr2); // Undefined Behavior + /// } + /// ``` #[unstable(feature = "ptr_offset_from", issue = "41079")] #[rustc_const_unstable(feature = "const_ptr_offset_from", issue = "41079")] #[inline] |