DDK Glossary - C

Glossary

cache

A high-speed buffer storage that contains frequently accessed instructions and data; it is used to reduce access time.

cached micro presentation space

A presentation space from a Presentation-Manager-owned store of micro presentation spaces. It can be used for drawing to a window only, and must be returned to the store when the task is complete.

CAD

Computer-Aided Design.

call

(1) The action of bringing a computer program, a routine, or a subroutine into effect, usually by specifying the entry conditions and jumping to an entry point. (I) (A) (2) To transfer control to a procedure, program, routine, or subroutine.

calling sequence

A sequence of instructions together with any associated data necessary to execute a call. (T)

Cancel

An action that removes the current window or menu without processing it, and returns the previous window.

cascaded menu

In the OS/2 operating system, a menu that appears when the arrow to the right of a cascading choice is selected. It contains a set of choices that are related to the cascading choice. Cascaded menus are used to reduce the length of a menu. See also cascading choice.

cascading choice

In SAA Common User Access architecture, a choice in a menu that, when selected, produces a cascaded menu containing other choices. An arrow (→) appears to the right of the cascading choice.

CASE statement

In PM programming, provides the body of a window procedure. There is usually one CASE statement for each message type supported by an application.

CDB

Command Descriptor Block. The structure used to communicate commands from a source to a destination.

CGA

Color graphics adapter.

chained list

A list in which the data elements may be dispersed but in which each data element contains information for locating the next. (T) Synonymous with linked list.

character

A letter, digit, or other symbol.

character box

(1) In computer graphics, the boundary that defines, in world coordinates, the horizontal and vertical space occupied by a single character from a character set. See also character mode. Contrast with character cell. (2) An imaginary parallelogram on a display surface that contains all parts of one graphic character. Synonymous with bounding box. (T) (3) The maximum area in which a symbol and all associated elements, such as a cursor, an underline, or space surrounding the symbol to separate it from other symbols, can be printed or displayed. Synonymous with character cell. (4) The imaginary parallelogram whose boundaries govern the size, orientation, and spacing of individual characters to be displayed on a graphics display device.

character cell

(1) The physical, rectangular space in which any single character is displayed on a screen or printer device. Position is addressed by row and column coordinates. Contrast with character box. (2) An addressable location on a display surface or printing medium. (3) The physical width and height in pels of a font. See also bounding box. (4) The imaginary box whose boundaries govern the size, orientation, and spacing of individual characters to be displayed on a workstation.

character code

The means of addressing a character in a character set, sometimes called code point.

character device

A device that performs I/O operations on one character at a time. Because character devices view data as a stream of bytes, character-device data cannot be randomly accessed. Character devices include the keyboard, mouse, and printer, and are referred to by name.

character mode

A mode that, in conjunction with the font type, determines the extent to which graphics characters are affected by the character box, shear, and angle attributes.

character set

(1) An ordered set of unique representations called characters; for example, the 26 letters of the English alphabet, Boolean 0 and 1, the set of symbols in the Morse code, and the 128 ASCII characters. (A) (2) All the valid characters for a programming language or for a computer system. (3) A group of characters used for a specific reason; for example, the set of characters a printer can print.

check box

In SAA Advanced Common User Access architecture, a square box with associated text that represents a choice. When a user selects a choice, an X appears in the check box to indicate that the choice is in effect. The user can clear the check box by selecting the choice again. Contrast with radio button.

check mark

(1) (D of C) In SAA Advanced Common User Access architecture, a symbol that shows that a choice is currently in effect. (2) The symbol that is used to indicate a selected item on a pull-down menu.

child process

In the OS/2 operating system, a process started by another process, which is called the parent process. Contrast with parent process.

child window

A window that appears within the border of its parent window (either a primary window or another child window). When the parent window is resized, moved, or destroyed, the child window also is resized, moved, or destroyed; however, the child window can be moved or resized independently from the parent window, within the boundaries of the parent window. Contrast with parent window.

choice

(1) An option that can be selected. The choice can be presented as text, as a symbol (number or letter), or as an icon (a pictorial symbol). (2) (D of C) In SAA Common User Access architecture, an item that a user can select.

chord

(1) To press more than one button on a pointing device while the pointer is within the limits that the user has specified for the operating environment. (2) (D of C) In graphics, a short line segment whose end points lie on a circle. Chords are a means for producing a circular image from straight lines. The higher the number of chords per circle, the smoother the circular image.

class

A way of categorizing objects based on their behavior and shape. A class is, in effect, a definition of a generic object. In SOM, a class is a special kind of object that can manufacture other objects that all have a common shape and exhibit similar behavior (more precisely, all of the objects manufactured by a class have the same memory layout and share a common set of methods). New classes can be defined in terms of existing classes through a technique known as inheritance.

class method

A class method of class <X> is a method provided by the metaclass of class <X>. Class methods are executed without requiring any instances of class <X> to exist, and are frequently used to create instances. In System Object Model, an action that can be performed on a class object.

class object

In System Object Model, the run-time implementation of a class.

class style

The set of properties that apply to every window in a window class.

client

(1) A functional unit that receives shared services from a server. (T) (2) A user, as in a client process that uses a named pipe or queue that is created and owned by a server process.

client area

The part of the window, inside the border, that is below the menu bar. It is the user's work space, where a user types information and selects choices from selection fields. In primary windows, it is where an application programmer presents the objects that a user works on.

client program

An application that creates and manipulates instances of classes.

client window

The window in which the application displays output and receives input. This window is located inside the frame window, under the window title bar and any menu bar, and within any scroll bars.

clip limits

The area of the paper that can be reached by a printer or plotter.

clipboard

In SAA Common User Access architecture, an area of computer memory, or storage, that temporarily holds data. Data in the clipboard is available to other applications.

clipping

In computer graphics, removing those parts of a display image or elements that lie outside a given boundary. (I) (A)

clipping area

The area in which the window can paint.

clipping path

A clipping boundary in world-coordinate space.

CLOCK$

Character-device name reserved for the system clock.

code page

An assignment of graphic characters and control-function meanings to all code points; for example, assignment of characters and meanings to 256 code points for an 8-bit code, assignment of characters and meanings to 128 code points for a 7-bit code.

code point

(1) Synonym for character code. (2) (D of C) A 1-byte code representing one of 256 potential characters.

code segment

An executable section of programming code within a load module.

color conversion

Changing one color format to another. Required, for example, when the source color format is different from the destination color format. When going from the monochrome color format to the color format, 1 (one) bits are converted to the image foreground color, and 0 (zero) bits are converted to the image background color. When going from color to monochrome, all pels that match the passed background color are converted to the image background color of the destination. All other pels are converted to the image foreground color of the destination. The color conversion takes place prior to any mix mode.

color dithering

See dithering.

color graphics adapter (CGA)

An adapter that simultaneously provides four colors and is supported by all IBM Personal Computer and Personal System/2 models.

command

The name and parameters associated with an action that a program can perform.

command area

An area composed of a command field prompt and a command entry field.

command code

Refers to a group of related commands that an adapter device driver can receive. All command codes have a prefix of "IOCC_". For example, common I/O requests (such as Read, Write, etc.) are grouped under the command code IOCC_EXECUTE_IO.

command data block

A data structure defined by the Small Computer System Interface standard to send commands to devices that conform to SCSI standards.

command descriptor block (CDB)

The structure used to communicate commands from a source to a destination.

command entry field

An entry field in which users type commands.

command line

On a display screen, a display line, sometimes at the bottom of the screen, in which only commands can be entered.

command mode

A state of a system or device in which the user can enter commands.

command modifier

A specific operation that an adapter device driver is to perform. All command modifiers have a prefix of "IOCM_". For example, an adapter device driver might receive an IOCC_EXECUTE_IO command with a command modifier of IOCM_READ.

command prompt

A field prompt showing the location of the command entry field in a panel.

Common Programming Interface (CPI)

Definitions of those application development languages and services that have, or are intended to have, implementations on and a high degree of commonality across the SAA environments. One of the three SAA architectural areas. See also Common User Access architecture.

Common User Access (CUA) architecture

Guidelines for the dialog between a human and a workstation or terminal. One of the three SAA architectural areas. See also Common Programming Interface.

compatibility kernel

The portion of the OS/2 kernel that exists to support DOS INT 20, 21, 25, 26, and 27 functions. It acts as an interface to common kernel functionality such as the file system.

compile

To translate a program written in a higher-level programming language into a machine language program.

composite window

A window composed of other windows (such as a frame window, frame-control windows, and a client window) that are kept together as a unit and that interact with each other.

computer-aided design (CAD)

The use of a computer to design or change a product, tool, or machine, such as using a computer for drafting or illustrating.

COM1, COM2, COM3

Character-device names reserved for serial ports 1 through 3.

CON

Character-device name reserved for the console keyboard and screen.

conditional cascaded menu

A pull-down menu associated with a menu item that has a cascade mini-push button beside it in an object's pop-up menu. The conditional cascaded menu is displayed when the user selects the mini-push button.

conditional compilation

Processing by the preprocessor of certain specified code in the file, depending on the evaluation of a specified condition.

container

In SAA Common User Access architecture, an object that holds other objects. A folder is an example of a container object. See also folder and object.

context hook

Similar to a "force flag" in earlier versions of OS/2. These are events, signaled by a virtual device driver, that are processed at task time. Forcing an IRET, and simulating an NMI, can fall into this category.

contextual help

In SAA Common User Access Architecture, help that gives specific information about the item the cursor is on. The help is contextual because it provides information about a specific item as it is currently being used. Contrast with extended help.

contiguous

Touching or joining at a common edge or boundary, for example, an unbroken consecutive series of storage locations.

control

In SAA Advanced Common User Access architecture, a component of the user interface that allows a user to select choices or type information; for example, a check box, an entry field, a radio button.

control area

A storage area used by a computer program to hold control information. (I) (A)

Control Panel

In the Presentation Manager, a program used to set up user preferences that act globally across the system.

control program

(1) The basic functions of the operating system, including DOS emulation and the support for keyboard, mouse, and video input/output. (2) A computer program designed to schedule and to supervise the execution of programs of a computer system. (I) (A)

controller sector buffer

One or more buffers, managed by a hardware adapter, to improve I/O transfer rates by helping to match a device and software timing requirements.

control window

A window that is used as part of a composite window to perform simple input and output tasks. Radio buttons and check boxes are examples.

control word

An instruction within a document that identifies its parts or indicates how to format the document.

coordinate space

A two-dimensional set of points used to generate output on a video display or printer.

Copy

A choice that places onto the clipboard, a copy of what the user has selected. See also Cut and Paste.

correlation

The action of determining which element or object within a picture is at a given position on the display. This follows a pick operation.

coverpage window

A window in which the application's help information is displayed.

CPI

Common Programming Interface.

critical extended attribute

An extended attribute that is necessary for the correct operation of the system or a particular application.

critical section

(1) In programming languages, a part of an asynchronous procedure that cannot be executed simultaneously with a certain part of another asynchronous procedure. (I) Note: Part of the other asynchronous procedure also is a critical section. (2) A section of code that is not reentrant; that is, code that can be executed by only one thread at a time.

CUA architecture

Common User Access architecture.

current position

In computer graphics, the position, in user coordinates, that becomes the starting point for the next graphics routine, if that routine does not explicitly specify a starting point.

Cut

In SAA Common User Access architecture, a choice that removes a selected object, or a part of an object, to the clipboard, usually compressing the space it occupied in a window. See also Copy and Paste.

cursor

A symbol displayed on the screen and associated with an input device. The cursor indicates where input from the device will be placed. Types of cursors include text cursors, graphics cursors, and selection cursors. Contrast with pointer and input focus.