Glossary H

Article
07/12/2006

handler

In OLE, a DLL that resides in a client process and performs some tasks on behalf of the server, while delegating other tasks back to the server itself.
In general, a routine that manages a common and relatively simple condition or operation, such as error recovery or data movement. See also message handler.

hash value

The value of a key that has been numerically manipulated to directly calculate either the location of its associated record in a table or the starting point for a search for the associated record. If the key value is a character string, each possible character is assigned a numeric code to permit the numerical manipulation. The manipulation performed on the key value is known as the hashing function.

head

The beginning of an item, such as a list, nonscrolling region, string, or transmission queue.
In hardware, the read/write mechanism in a disk drive or magnetic tape drive, or the printing mechanism in a printer.

header control

In MFC, a window usually positioned above columns of text or numbers. The header control contains a title for each column, and it can be divided into parts. The user can drag the dividers that separate the parts to set the width of each column.

header file

An external source file, identified at the beginning of a program, that contains commonly used data types and variables used by functions in the program. The #include directive is used to tell the compiler to insert the contents of a header file into the program. See also C++ header file.

heap

Or free store. A portion of memory reserved for a program to use for the temporary storage of data structures whose existence or size cannot be determined until the program is running. The program can request free memory from the heap to hold such elements, use it as necessary, and later free the memory.
In sorting, a partially ordered complete binary tree.

heap allocation

Reserving memory for the needs of the program. See also heap, stack.

Help context

A string and a number (Help context ID) that an application passes during a call to Windows Help in order to locate and display a Help topic. See also Help map file, Help project file.

Help file

A file that contains text and graphics needed to communicate online information about an application. Each help file contains one or more topics a user can select by clicking hot spots, using the keyword search, or browsing through topics. Help files have a .HLP filename extension. See also Help topic.

Help map file

A file that defines Help context IDs corresponding to the IDs of dialog boxes, menu commands, and other resources in an application. A custom build rule on a project’s RESOURCE.H file in AppWizard projects calls the MAKEHM tool to generate the .HM file based on any change in the contents of the RESOURCE.H file (the MAKEHELP.BAT file performed this function in prior versions of Visual C++). The Help map file has a .HM filename extension. See also Help project file.

Help project file

A project file that controls how the Windows Help Compiler creates a Help (.HLP) file from topic files. The Microsoft Help Workshop is used to create a Help project file. The filename extension of a Help project file is .HPJ.

Help topic

The primary unit of information in a Help (.HLP) file. A topic is a self-contained body of text and graphics, similar to a page in a book. Unlike a page, however, a topic can hold as much information as you require. If there is more information in a topic than the Help window can display, scroll bars appear to let the user scroll through the information.

helper function

A function that calls a sequence of other functions or interface methods publicly available in the OLE SDK and MFC templates. Helper functions are a convenient way to call frequently used sequences of function or method calls that accomplish common tasks.

hexadecimal

Or hex. The base-16 counting system, whose digits are 0 through F. The letters A through F represent the decimal numbers 10 through 15. Two hex digits are needed to represent 1 byte. See also binary.

hidden text

In a document file, special characters that are not normally printed or displayed on the screen. For example, in a rich-text format (.RTF) file for a Help topic, the following hidden text string generates a jump to another Help topic:

Jump textcontextstring@d:\path\file.hlp

high order

In a group of bits or bytes, the one that carries the most weight or significance. Within a byte, the leftmost bit is the high-order bit. Within a group of bytes, the byte-ordering convention (big-endian or little-endian) determines the position of the high-order byte.

high-performance file system

A fixed-disk file system that organizes the disk into volumes, rather than partitions and logical drives. HPFS supports long, mixed-case filenames and extended attributes, and implements several levels of caching, for improved operating-system performance. The IBM OS/2 operating system supports HPFS. See also file allocation table file system, New Technology file system (NTFS).

highlighting

Altering the appearance of displayed characters as a means of calling attention to them — for example, by displaying them with higher intensity or by using reverse video (dark on light instead of light on dark, or vice versa). Highlighting is often used to denote characters to be deleted, copied, or otherwise acted upon.

hit count

The number of times a function or line of source code is called (or hit), as reported by the profiler when analyzing a program at run time. See also function profiling, line counting, line profiling.

hit-test code

A code that determines the location of the cursor. For example, HTLEFT means the cursor is in the left border of the window; HTMAXBUTTON means the cursor is in a Maximize button.

home page

The main page of a Web site as generated by the developer of the site. Although the home page is often the first page a visitor to the site sees, it is not the same as start page.

hook

A point in the Windows message-handling mechanism where an application can install a subroutine to monitor the message traffic in the system and process certain types of messages before they reach the target window procedure.
More generally, a location in a routine or program at which the programmer can connect or insert other routines for the purpose of debugging or enhancing functionality.

hook procedure

An application-installed procedure that monitors the system for events associated with either a specific thread or all threads in the system. For example, the hook code WH_GETMESSAGE installs a hook procedure that monitors messages posted to a message queue. See also callback function.

hot key

In Windows, an application-defined key combination used to obtain high-priority keyboard input from the user. For example, an application can have a hot key that allows the user to cancel a lengthy operation.
A key combination that the user can create to perform an action quickly. See also accelerator key.

hot spot

The pixel in a cursor that marks the exact screen location affected by a mouse action, such as a button click. Mouse messages include the coordinates of the hot spot.

hourglass cursor

A cursor displayed in the form of an hourglass that indicates that the program is performing a lengthy task. The cursor can be displayed as a large hourglass, or as a smaller hourglass with an arrow.

HPFS

HTML

A markup language derived from SGML. Used to create a text document with formatting specifications that tells a software browser how to display the page or pages included in the document.

HTTP

The Internet protocol used by World Wide Web browsers and servers to exchange information. The protocol makes it possible for a user to use a client program to enter a URL (or click a hyperlink) and retrieve text, graphics, sound, and other digital information from a Web server. HTTP defines a set of commands and uses ASCII text strings for a command language. An HTTP transaction consists of a connection, a request, a response, and a close.

HTTP server

Or Web server. A server that runs a Hypertext Transfer Protocol service or application. This protocol defines the procedures used when connecting a Web browser to a Web server.

hyperlink

The means used to jump to another Web page. It consists of both the display text the user sees and the URL of the reference. See also hypertext link.

hyperlink address

The path to an object, document, or page. A hyperlink address can be a URL or a UNC network path. Can also contain display text or sublocation information (for example, a database object, Word bookmark, or Microsoft Excel cell range to which the address points).

hyperlink base

A partial path based on a user-defined path. Use a hyperlink base if you want to move either the file that contains the hyperlink or the destination file separately and still maintain the hyperlink.

hypertext link

In a Web document, this is a reference to another Web document. The user does not actually see a URL in the document; instead, a highlighted reference contains a pointer to a link. The user clicks on the highlighted reference and the desired Web page is automatically retrieved. See also hyperlink.

Hypertext Markup Language