SimConnect Go SDK

L:vars

pkg/lvars writes local variables (L:vars) on the user aircraft through SimConnect (Windows only). An application uses it to signal other add-ons (the aircraft’s gauges, GSX, FSUIPC, an in-sim package) and to write the variables they document as settable.

An L:var exists once it is written: writing a new name creates it, and every other client reads it. Measured live in MSFS 2024: L:MYCREW_TEST written as 42 by one connection was read as 42 by another.

Writer

w := lvars.NewWriter(client, defBase, 0) // definitions defBase … defBase+63
if err := w.Set("MYCREW_BOARDING", 1); err != nil { // or "L:MYCREW_BOARDING"
    log.Println(err)
}
_ = w.Set(gsx.SetPassengers, 111) // a GSX setting

// on a new connection:
w.Reset(newClient)
  • NewWriter(client, defBase, max): client is anything with AddToDataDefinition and SetDataOnSimObject (lvars.Client: an engine.Engine or the manager). Each name gets a data definition of its own, from defBase to defBase+max-1; max 0 means DefaultMax (64). Keep that block clear of your other definition IDs.
  • Set(name, value): writes value (a float64, unit number) to the user aircraft. The L: prefix is optional. The first write of a name defines it on this connection; once max names are defined, a new name returns an error.
  • Reset(client): forgets the definitions, since a new connection has none; a non-nil client replaces the old one. Call it on every reconnect.

A Writer is safe for concurrent use.

Reading

pkg/lvars only writes. To read L:vars, list them in an aircraft profile of pkg/systems (its values land in State.Values by name); GSX’s own are read by pkg/gsx.

See also