Pointer (computer Programming)
I do consider assignment statements and pointer variables to be among computer science's most valuable treasures.Donald Knuth, Structured Programming with go to Statements
In computer science, a pointer is a programming language data type whose value refers directly to (or "points to") another value stored elsewhere in the computer memory using its address. For high-level programming languages, pointers effectively take the place of general purpose registers in low-level languages such as assembly language or machine code, but may be in available memory. A pointer references a location in memory, and obtaining the value at the location a pointer is known as dereferencing the pointer. A pointer is a simple, more concrete implementation of the more abstract reference data type. Several languages support some type of pointer, although some have more restrictions on their use than others. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number.
Pointers to data significantly improve performance for repetitive operations such as traversing strings, lookup tables, control tables and tree structures. In particular, it is often much cheaper in time and space to copy and dereference pointers than it is to copy and access the data to which the pointers point.
Pointers are also used to hold the addresses of entry points for called subroutines in procedural programming and for run-time linking to dynamic link libraries (DLLs). In object-oriented programming, pointers to functions are used for binding methods, often using what are called virtual method tables.
While "pointer" has been used to refer to references in general, it more properly applies to data structures whose interface explicitly allows the pointer to be manipulated (arithmetically via pointer arithmetic) as a memory address, as opposed to a magic cookie or capability where this is not possible. Because pointers allow both protected and unprotected access to memory addresses, there are risks associated with using them particularly in the latter case. Primitive pointers are often stored in a format similar to an integer; however, attempting to dereference or "look up" a pointer whose value was never a valid memory address would cause a program to crash. To alleviate this potential problem, as a matter of type safety, pointers are considered a separate type parameterized by the type of data they point to, even if the underlying representation is an integer. Other measures may also be taken.
Read more about Pointer (computer Programming): Formal Description, Use in Data Structures, Use in Control Tables, Architectural Roots, Uses, Typed Pointers and Casting, Making Pointers Safer, Null Pointer, Autorelative Pointer, Based Pointer, Multiple Indirection, Function Pointer, Wild Pointers, Wild Branch, Simulation Using An Array Index
Famous quotes containing the word pointer:
“The hardiest skeptic who has seen a horse broken, a pointer trained, or has visited a menagerie or the exhibition of the Industrious Fleas, will not deny the validity of education. A boy, says Plato, is the most vicious of all beasts; and in the same spirit the old English poet Gascoigne says, A boy is better unborn than untaught.”
—Ralph Waldo Emerson (18031882)