A stale pointer bug, otherwise known as an aliasing bug, is a class of subtle programming errors that can arise in code that does dynamic memory allocation, especially via the malloc

Malloc

C dynamic memory allocation refers to performing dynamic memory allocation in the C via a group of functions in the C standard library, namely malloc, realloc, calloc and free....

 function or equivalent.

If several pointers address (are "aliases for") a given hunk of storage, it may happen that the storage is freed or reallocated (and thus moved) through one alias and then referenced through another, which may lead to subtle (and possibly intermittent) lossage depending on the state and the allocation history of the malloc arena. This bug can be avoided by never creating aliases for allocated memory, by controlling the dynamic scope

Scope (programming)

In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes. The type of scope determines what kind of entities it can contain and how it affects them—or semantics...

 of references to the storage so that none can remain when it is freed, or by use of a garbage collector

Garbage collection (computer science)

In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program...

, in the form of an intelligent memory-allocation library or as provided by higher-level languages

High-level programming language

A high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or be from the specification of the program, making the process of...

, such as Lisp

Lisp programming language

Lisp is a family of computer programming languages with a long history and a distinctive, fully parenthesized syntax. Originally specified in 1958, Lisp is the second-oldest high-level programming language in widespread use today; only Fortran is older...

.

The term "aliasing bug" is nowadays associated with C

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

 programming, but it was already in use in a very similar sense in the ALGOL

ALGOL

ALGOL is a family of imperative computer programming languages originally developed in the mid 1950s which greatly influenced many other languages and became the de facto way algorithms were described in textbooks and academic works for almost the next 30 years...

 60 and Fortran

Fortran

Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...

programming language communities in the 1960s.