UNINITIALIZED_VAR_USED

Severity: warn. PLCopen: CP3 — every variable shall be initialised before being used.

A local variable (VAR, VAR_OUTPUT, VAR_TEMP) is read at a source line that comes before its first assignment, and the declaration has no explicit initial value. The value the read sees depends on the runtime's "uninitialised" semantics — often zero, sometimes garbage from a previous scan — and the resulting behaviour is at best undefined.

Settings. No check-specific config. This is a source-position heuristic and does not model control flow — a conditional initialiser (IF cond THEN x := 1; END_IF; y := x;) may produce false positives. The audit roadmap notes that closing that gap needs a full reaching-defs pass.

Trigger.

FUNCTION_BLOCK FB_U
VAR
    x : INT;
    y : INT;
END_VAR
y := x + 1;     (* fires — x is read before any assignment *)
x := 1;
END_FUNCTION_BLOCK

Not a trigger. Initial value at the declaration silences the check:

VAR
    x : INT := 0;
END_VAR
y := x + 1;     (* quiet *)

The bot posts.

🟧 warn  UNINITIALIZED_VAR_USED
'x' is read before any assignment (PLCopen CP3)

Fix. Add an initial value to the declaration (x : INT := 0;), or move the assignment above the first read.