|
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, for references to data stored in memory on a given system, a reference is implemented as the physical address of where the data is stored in memory or in the storage device. For this reason, a reference is often erroneously confused with a ''pointer'' or ''address'', and is said to "point to" the data. However a reference may also be implemented in other ways, such as the offset (difference) between the datum's address and some fixed "base" address, as an index into an array, or more abstractly as a handle. More broadly, in networking, references may be ''network'' addresses, such as URLs. 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. References can cause significant complexity in a program, partially due to the possibility of dangling and wild references and partially because the topology of data with references is a directed graph, whose analysis can be quite complicated. ==Benefits== References increase flexibility in where objects can be stored, how they are allocated, and how they are passed between areas of code. As long as one can access a reference to the data, one can access the data through it, and the data itself need not be moved. They also make sharing of data between different code areas easier; each keeps a reference to it. The mechanism of references, if varying in implementation, is a fundamental programming language feature common to nearly all modern programming languages. Even some languages that support no direct use of references have some internal or implicit use. For example, the call by reference calling convention can be implemented with either explicit or implicit use of references. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reference (computer science)」の詳細全文を読む スポンサード リンク
|