Tombstones are a mechanism to detect
dangling pointer
Dangling pointers and wild pointers in computer programming are pointers that do not point to a valid object of the appropriate type. These are special cases of memory safety violations. More generally, dangling references and wild references are ...
s and mitigate the problems they can cause in computer programs. Dangling pointers can appear in certain computer
programming language
A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language.
The description of a programming l ...
s, e.g.
C,
C++ and
assembly languages.
A tombstone is a structure that acts as an intermediary between a
pointer
Pointer may refer to:
Places
* Pointer, Kentucky
* Pointers, New Jersey
* Pointers Airport, Wasco County, Oregon, United States
* The Pointers, a pair of rocks off Antarctica
People with the name
* Pointer (surname), a surname (including a list ...
and its target, often
heap-dynamic data in
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered ...
. The pointer – sometimes called the
handle
A handle is a part of, or attachment to, an object that allows it to be grasped and manipulated by hand. The design of each type of handle involves substantial ergonomic issues, even where these are dealt with intuitively or by following tr ...
– points only at tombstones and never to its actual target. When the data is deallocated, the tombstone is set to a
null
Null may refer to:
Science, technology, and mathematics Computing
*Null (SQL) (or NULL), a special marker and keyword in SQL indicating that something has no value
*Null character, the zero-valued ASCII character, also designated by , often used ...
(or, more generally, to a value that is illegal for a pointer in the given runtime environment), indicating that the variable no longer exists. This mechanism prevents the use of invalid pointers, which would otherwise acc