Definition of Terms

The following is a list of many of the terms used both in this guide and in the Windows API. Please refer to it whenever you are unclear about the meaning of a certain term.

Alternate Declare

A secondary Declare sometimes required in Visual Basic as a result of the language's syntax. Some API functions sometimes require null data to be passed instead of a data structure, and setting all of the structure's members to 0 does not work. The alternate Declare links to the same function under an assumed name and uses a modified parameter list to allow a 0 or some other null character to be passed instead of the structure. See also: Declare.

Declare

The command used in Visual Basic to create a link between the program and an API function. The Declare identifies the name of the function, the DLL it is located in, and the list of parameters to be passed to it. See also: Alternate Declare.

Device Context

A number that identifies some device under Windows. Devices usually deal with input or output, or both. Many devices are physical hardware, although all windows are also considered devices. The device context is used whenever I/O information is read from or written to the device. See also: Handle, Pointer.

Handle

A number that identifies some object under Windows. Handles can identify most kinds of object, including registry keys, files, memory blocks, and windows. Handles usually apply when the exact physical location of an object is unknown or unimportant, although the object itself is. See also: Device Context, Pointer.

Pointer

A number that identifies a specific memory address. Pointers differ from handles to memory blocks because whereas the handle refers to a block of memory whose exact physical location may vary, the pointer identifies the specific physical location of where it starts. Visual Basic implicitly passes strings, data structures, and all ByRef variables by passing a pointer to the variable's memory address to the function. See also: Device Context, Handle.