Add a variable | ForgeIEC

Overview

The FAddVariableDialog is the modal window used to add a new variable to a POU or the pool. It collects every field in a single step and shows a live preview of the resulting IEC ST declaration right below the form — what you type immediately renders as a finished VAR ... END_VAR snippet.

The dialog runs in two modes:

Add mode: empty fields, OK creates a new variable. Reached via the plus icon in the Variables panel or Ctrl+N in the POU editor.
Edit mode: double-click an existing variable in the panel — same dialog, every field pre-filled.

Fields

Field	Required	Meaning
Name	yes	Programmer-visible name. Validated against IEC identifier rules (letter + letters/digits/`_`). Used for bulk creation with a range pattern (see below).
Type	yes	Combo with IEC elementary types, standard FBs, project FBs, user data types. Array creation is handled by the wrapper checkbox.
Direction	depends on POU	Var-class — see below.
Initial	no	Initial value (`FALSE`, `0`, `T#100ms`, `'OFF'`).
Address	no	Only for VarList POUs. Empty = `pool->nextFreeAddress` auto-allocates on creation.
Retain	no	Checkbox — RETAIN, value survives a power cycle.
Constant	no	Checkbox — `VAR CONSTANT`, not writable at runtime.
Array wrapper	no	Wraps the selected type in `ARRAY [..] OF`.
Documentation	no	Free-text comment, stored as `<documentation>` in PLCopen XML.

Range pattern for bulk creation

Instead of typing LED_0, LED_1, … LED_7 individually you can specify a range pattern in the name field:

Input	Effect
`LED_0..7`	Creates eight variables `LED_0` through `LED_7`.
`LED_0-7`	Synonym, same effect.
`Sensor_1..3`	Creates three variables `Sensor_1` through `Sensor_3`.

On every bulk creation the address is incremented if it is set: %QX0.0 → %QX0.0, %QX0.1, …, %QX0.7.

Array wrapper checkbox

If you want one variable declared as an array, tick the array checkbox. Two spin boxes appear for the index range and the type is wrapped at runtime as ARRAY [..] OF <type>.

Type combo	Array checkbox	Index range	Resulting declaration
`INT`	off	—	`: INT;`
`INT`	on	`0..7`	`: ARRAY [0..7] OF INT;`
`BOOL`	on	`1..16`	`: ARRAY [1..16] OF BOOL;`
`T_Motor` (user struct)	on	`0..3`	`: ARRAY [0..3] OF T_Motor;`

The wrapper deliberately lives on a checkbox rather than in the type combo — that keeps the combo uncluttered and lets you build arrays of anything without searching the combo.

Type combo

The combo aggregates four sources into a single list:

IEC elementary types: BOOL, BYTE, WORD, DWORD, LWORD, INT, DINT, LINT, UINT, UDINT, ULINT, REAL, LREAL, TIME, DATE, TIME_OF_DAY, DATE_AND_TIME, STRING, WSTRING.
Standard FBs from the library: TON, TOF, TP, R_TRIG, F_TRIG, CTU, CTD, CTUD, SR, RS, …
Project function blocks — every FB declared in the current project (user library).
User data types from <dataTypes>: STRUCTs, enums, aliases.

ARRAY templates do not appear in the combo — they go through the wrapper checkbox.

Direction (var-class) per POU type

Which direction values are offered depends on the POU type:

POU type	Available direction
`PROGRAM` / `FUNCTION_BLOCK` / `FUNCTION`	`VAR` / `VAR_INPUT` / `VAR_OUTPUT` / `VAR_IN_OUT` / `VAR_TEMP`
`GlobalVarList` (GVL)	Fixed `VAR_GLOBAL` — combo hidden.
`AnvilVarList`	Fixed `VAR_GLOBAL` (auto-generated) — combo hidden.
Pool globals (no POU container)	No direction — the `%I`/`%Q` address sets it implicitly.

Edit mode

Double-clicking an existing variable in the Variables panel opens the same dialog. Every field is pre-filled; on OK changes are routed through pou->renameVariable / pool->rebind (so the byAddress indices stay in sync). The dialog detects edit mode by existing != nullptr.

Example — 8 LEDs in one block

Eight output LEDs as pool variables, in a single step:

Name: LED_0..7
Type: BOOL
Direction: hidden (pool global)
Address: %QX0.0 (auto-increment)
Initial: FALSE

OK creates eight pool entries:

LED_0  AT %QX0.0 : BOOL := FALSE;
LED_1  AT %QX0.1 : BOOL := FALSE;
LED_2  AT %QX0.2 : BOOL := FALSE;
LED_3  AT %QX0.3 : BOOL := FALSE;
LED_4  AT %QX0.4 : BOOL := FALSE;
LED_5  AT %QX0.5 : BOOL := FALSE;
LED_6  AT %QX0.6 : BOOL := FALSE;
LED_7  AT %QX0.7 : BOOL := FALSE;

The eight variables can then be selected in the Variables panel and assigned to an HMI group via a bulk operation — e.g. Set HMI Group... -> Frontpanel.

Variable management — the Variables panel with columns, filters and bulk operations.
Project file format — how the pool is persisted as an <addData> block in PLCopen XML.