The software maintains a series of system variables that represent either fixed values ($ZimOS) or values that fluctuate dynamically with the current status of the software ($InTransaction) or of application objects (ThisWindow.WindowTag).

System variables resemble global variables in nature. The software automatically sets or resets the values of system variables to reflect the status of the software and the current application. In some cases, an application program can also reset them.

A system variable name can be used as an atomic expression denoting the value currently held in the memory location associated with the variable. A system variable name can be used almost anywhere that a literal can be used.

Available System Variables

System variables are categorized into those that supply information about windows, those that supply information about menus, those that supply information about forms, and those that supply general information. Some system variables are “binary” in nature in that they evaluate only to ‘1’ ($True) or ‘0’ ($False), while others may be set to a variety of values.

General-use System Variables with “Permanent” Values

Given a particular version of the software, the following system variables have the same value at all times during an application session:

General-use System Variables with Values Derived from the Operating System

The software sets the values of the following system variables based on current values obtained from the operating system:

System Variables Periodically Set/Reset by the Software or the Application System

The values of these variables are set and reset depending on conditions encountered during execution of the application. An application program can assign a value to any of these variables at any time; however, the assigned value can be overwritten as conditions subsequently change during the application session.

Last Callback Event

Event is a data structure that provides information about the application environment the time of the most recent callback even. Each variable in the structure provides one item of information. The values of these variables are reset each time a callback event returns control to the application program. An application program can assign a value to any of these variables at any time; however, the assigned value is overwritten the next time that a callback event occurs.

Text Cursor Positioning

Error Status

Other Status Conditions

External Programs

Security

System Variables Concerned with Windows

Last Event in the Current Window

ThisWindow is a data structure that provides information about the state of the application environment and of the current window at the time of the last event in that window. Each variable in the structure provides one item of information. The values of these variables are reset each time a window becomes the current window. An application program can assign a value to any of these variables at any time; however, the assigned value is overwritten the next time that another window becomes the current window.

Miscellaneous

System Variables Concerned with Menus

Last Event in the Current Menu

ThisMenu is a data structure that provides information about the state of the software environment and of the current menu at the time of the last event in that menu. Each variable in the structure provides one item of information. The values of these variables are reset each time that FORM or MENU INPUT terminates. An application program can assign a value to any of these variables at any time; however, the assigned value is overwritten the next time that FORM or MENU INPUT terminates.

System Variables Concerned with Forms

Last Event in the Current Form/Display

ThisForm is a data structure that provides information about the state of the current form/display at the time of the last event in the current window. Each variable in the structure provides one item of information. The values of these variables are reset each time that FROM or MENU INPUT terminates, An application program can assign a value to any of these variables at any time; however, the assigned value is overwritten the next time that FORM or MENU INPUT terminates.