Thanks, but none of your links is a usable connection status flag or similar function. But if you still find one, please post it here. I know that it is difficult.

FXCM does not detect interruptions, only logouts or server outages on their side. The LastErrorCode by MT4 can return ERR_NO_CONNECTION when sending an order. But it's no good idea to send orders for testing the connection status.

https://docs.mql4.com/check/isconnected

This seems to the flag for MT4.

LastError() code can also be used - to signal a relevant error.

Both MultiCharts and SierraChart use IB API error codes to determine the status of connection. SC then exposes this further to a user via a variable at run-time.

JCL,

is there any update on this - for MT4 and IB?

This would only confirm the connection between DTC client and DTC server and not necessarily the layer behind it (i.e. Sierra Chart's connection to its server).