R
redirect
  To associate files with the input or output of commands.
reentrant
  The attribute of a program or routine that allows the same copy of a program or routine to be used concurrently by two or more tasks.
reference class
  A class that links a concrete class to an abstract class. Reference classes make polymorphism possible with the Collection Classes. See abstract class, concrete class, polymorphism.
register
  A storage area commonly associated with fast-access storage, capable of storing a specified amount of data such as a bit or address.
register storage class specifier
  A specifier that indicates to the compiler within a block scope data definition or a parameter declaration that the object being described will be heavily used.
register variable
  A variable defined with the register storage class specifier. Register variables have automatic storage.
regular expression
  (1) A mechanism to select specific strings from a set of character strings. (2) A set of characters, metacharacters, and operators that define a string or group of strings in a search pattern. (3) A string containing wildcard characters and operations that define a set of one or more possible strings.
regular file
  A file that is a randomly accessible sequence of bytes, with no further structure imposed by the system. X/Open, I.
relation
  An unordered flat collection class that uses keys, allows for duplicate elements, and has element equality. See key access, unordered collection.
renderer
  An object that renders data using a particular mechanism, such as using files or shared memory. It contains definitions of supported rendering mechanisms and formats and types.
rendering
  The transfer or re-creation of the dragged object from the source window to the target window.
resource
  (1) Any facility of a computing system or operating system required by a job or task, including main storage, input/output devices, the processing unit, data sets, and control or processing programs. (2) A binary data item that is linked to an executable file, a DLL, or some other binary file. Typically a resource defines an interface component such as a dialog box, a menu, an icon, a font, a bitmap, or a cursor. (3) Any element that requires translation, such as messages or online help.
resource file
  A source file or compiled file that defines the resources that are used by an application. IBM C/C++ Compilers recognizes uncompiled resource files by the file extension .rc. A compiled resource file has the extension .res.
response file
  A file that acts as an extension of command-line input, providing options and parameters as input to a component.
return
  A language construct that ends an execution sequence in a procedure. IBM.
REXX
  Restructured Extended Executor. A general-purpose, procedural language for end-user personal programming. It is useful for application macros. IBM.
RGB
  Red, green, blue. A method of processing color images according to their red, green, and blue color content.
RMFs
  Rendering mechanisms and formats.
root
  A node that has no parent. All other nodes of a tree are descendants of the root. See tree, node, child node, parent node.
RTTI
  See run-time type identification.
run-time library
  A compiled collection of functions whose members can be referred to by an application program during run-time execution. It includes all the functions defined for ANSI C, and a lot more.
run-time type identification (RTTI)
  A mechanism in the C++ language for determining the class of an object at run time. It consists of two operators: one for determining the run-time type of an object (typeid), and one for doing type conversions that are checked at run time (dynamic_cast). A type_info class describes the RTTI available and defines the type returned by the typeid operator.
rvalue
  An expression that cannot have a value assigned to it. The result of calling a function that does not return a reference. Rvalues always have complete types or the void type. Contrast with lvalue.