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A dangling pointer is a pointer that does not point to a valid object and consequently may make a program crash or behave oddly. In the Pascal or C programming languages, pointers that are not specifically initialized may point to unpredictable addresses in memory. The following example code shows a dangling pointer:
When a dangling pointer is used after it has been freed without allocating a new chunk of memory to it, this becomes known as a "use after free" vulnerability. [4] For example, CVE-2014-1776 is a use-after-free vulnerability in Microsoft Internet Explorer 6 through 11 [5] being used by zero-day attacks by an advanced persistent threat. [6]
The C99 Language Specification ( ISO9899:1999 ) has the following warning in section 6.3.2.3 Pointers : "A pointer to an object or incomplete type may be converted to a pointer to a different object or incomplete type. If the resulting pointer is not correctly aligned for the pointed-to type, the behavior is undefined."
However, the language also offers various alternatives to complex forms of memory management. Reference counting functionality is provided by the Rc and Arc types, which are non-atomic and atomic respectively. For example, the type Rc<T> provides shared ownership of a value of type T, allocated on the heap for multiple references to its data. [22]
In assembly, C, C++, Pascal, Modula2 and other languages, a callback function is stored internally as a function pointer. Using the same storage allows different languages to directly share callbacks without a design-time or runtime interoperability layer. For example, the Windows API is accessible via multiple languages, compilers and assemblers.
In computer science, a tagged pointer is a pointer (concretely a memory address) with additional data associated with it, such as an indirection bit or reference count.This additional data is often "folded" into the pointer, meaning stored inline in the data representing the address, taking advantage of certain properties of memory addressing.
Smart pointers are opaque data structures that act like pointers but can only be accessed through particular methods. A handle is an abstract reference, and may be represented in various ways. A common example are file handles (the FILE data structure in the C standard I/O library), used to abstract file content.
Many approaches to flow-insensitive pointer analysis can be understood as forms of abstract interpretation, where heap allocations are abstracted by their allocation site (i.e., a program location). [6] Flow-insensitive pointer analyses often abstract possible runtime allocations by their allocation site.