Glossary

E
EBCDIC: See extended binary-coded decimal interchange code.
element: The component of an array, subrange, enumeration, or set.
element equality: A relation that determines whether two elements are equal.
element function: A function, called by a member function, that accesses the elements of a class.
else clause: The part of an if statement that contains the keyword else, followed by a statement. The else clause provides an action that is executed when the if condition evaluates to zero (false). IBM.
empty string: (1) A string whose first byte is a null byte. See null string. X/Open. (2) A character array whose first element is a null character. I.
encapsulation: (1) A method for protecting parts of a program and data from unwanted access or alteration by other parts. (2) The hiding of the internal representation of objects and implementation details from the client program.
encode: Convert data to machine-readable format. The three steps in converting an analog signal to a digital signal are sampling, quantizing, and encoding.
enqueue: An operation that adds an element as the last element to a queue. See dequeue.
entry point: In assembler language, the address or label of the first instruction that is executed when a routine is entered for execution.
enumeration constant: An identifier that is defined in an enumerator and that has an associated constant value of its enumeration type.
enumeration data type: A type that represents a set of enumeration constants. Each enumeration constant has an associated constant value.
enumeration tag: The identifier that names an enumeration data type.
enumerator: In the C and C++ languages, an enumeration constant and its associated value. IBM.
environment variable: Any of a number of variables that describe the way an operating system is going to run or the devices it is going to recognize. IBM.
equality collection: (1) An abstract class with the property of element equality. (2) Any collection that has element equality.
equality key collection: An abstract class with the properties of element equality and key equality.
equality key sorted collection: An abstract class with the properties of element equality, key equality, and sorted elements.
equality sequence: A sequentially ordered flat collection with element equality.
equality sorted collection: An abstract class with the properties of element equality and sorted elements.
equivalence class: (1) A grouping of characters that are considered equal for the purpose of collation; for example, many languages place an uppercase character in the same equivalence class as its lowercase form, but some languages distinguish between accented and unaccented character forms for the purpose of collation. IBM. (2) A set of collating elements with the same primary collation weight. Elements in an equivalence class are typically elements that naturally group together, such as all accented letters based on the same base letter. The collation order of elements within an equivalence class is determined by the weights assigned on any subsequent levels after the primary weight. X/Open.
escape sequence: (1) A representation of a character. An escape sequence contains the \ symbol followed by one of the characters: a, b, f, n, r, t, v, ', ", x, \, or followed by one or more octal or hexadecimal digits. (2) A sequence of characters that represent, for example, nonprinting characters, or the exact code point value to be used to represent variant and nonvariant characters regardless of code page. (3) In the C and C++ languages, an escape character followed by one or more characters. The escape character indicates that a different code, or a different coded character set, is used to interpret the characters that follow. Any member of the character set used at run time can be represented using an escape sequence. (4) A character that is preceded by a backslash character and is interpreted to have a special meaning to the operating system. (5) A sequence sent to a terminal to perform actions such as moving the cursor, changing from normal to reverse video, and clearing the screen. IBM.
event: (1) Any user action (such as a mouse click) or system activity (such as screen updating) that provokes a response from the application. (2) In the Windows operating system, a synchronization kernel object used to signal that an operation has completed. See kernel object, critical section, mutex, semaphore, manual-reset event, auto-reset event.
exception: (1) A user or system error detected by the system and passed to an operating system or user exception handler. (2) In the C++ language, any user, logic, or system error detected by a function that does not itself deal with the error but passes the error on to a handling routine (also called "throwing the exception"). See signal.
exception handler: (1) A function that is invoked when an exception is detected, and that either corrects the problem and returns execution to the program, or terminates the program. (2) In the C++ language, a catch block that catches a C++ exception when it is thrown from a function in a try block.
exception handling: A type of error handling that allows control and information to be passed to an exception handler when an exception occurs. Under the OS/2 operating system, exceptions are generated by the system and handled by user code. In the C++ language, try, catch, and throw expressions are the constructs used to implement C++ exception handling. See structured exception handling.
expression: A representation of a value; for example, variables and constants that appear alone or in combination with operators are expressions.
extended binary-coded decimal interchange code (EBCDIC): A coded character set of 256 eight-bit characters. IBM.
extension: An element or function not included in the standard language. See file extension.
external data definition: A definition of a variable appearing outside a function. The defined object is accessible to all functions that follow the definition and are located within the same source file as the definition.
eyecatcher: A recognizable sequence of bytes that determines which parameters were passed in which registers. This sequence is used for functions that have not been prototyped or have a variable number of parameters.