Reference (computer Science)

Reference (computer Science)

In computer science, a reference is a value that enables a program to indirectly access a particular datum, such as a variable or a record, in the computer's memory or in some other storage device. The reference is said to refer to the datum, and accessing the datum is called dereferencing the reference.

A reference is distinct from the data itself. Typically, a reference is the physical address of where the data is stored in memory or in the storage device. For this reason, a reference is often called a pointer or address, and is said to point to the data. However a reference may also be the offset (difference) between the datum's address and some fixed "base" address, or an index into an array.

The concept of reference must not be confused with other values (keys or identifiers) that uniquely identify the data item, but give access to it only through a non-trivial lookup operation in some table data structure.

References are widely used in programming, especially to efficiently pass large or mutable data as arguments to procedures, or to share such data among various uses. In particular, a reference may point to a variable or record that contains references to other data. This idea is the basis of indirect addressing and of many linked data structures, such as linked lists.

A reference may be compared to a street address, such as "12 Main Street" or "three houses down the road on the left side". Going to the building with that address is analogous to dereferencing the reference. The name "Bob and Joe's Car Shop" might be a unique identifier for the same building, but cannot be compared to a data reference, because finding the building with that name requires a non-trivial search or a lookup in some directory.