I am working on some legacy code on Windows for a desktop app in “C.
The client needs to know the geo-location of the user who is running the application.
I have the geo-location code all working (using MaxMind: http://dev.maxmind.com/).
But now I’m looking for help in getting their external IP.
From all the discussions on this topic throughout SO and elsewhere it seems that there is a way to do this by connecting to a “reliable” host (server) and then doing some kind of lookup. I’m not too savvy on WinSock but this is the technology that may be the simplest to use.
Another option is to use WinHttpConnect technology.
Both have “C” interfaces.
Thank you for your support and suggestions.
You can write a simple web service that checks the IP address(es) that the program presents when connecting to that web service.
Look at http://whatismyip.com for an example.
Note that multiple addresses can be presented by the HTTP protocol if there are proxy servers along the route.
You can design your simple web service to get the IP of the client. See
How do I get the caller's IP address in a WebMethod?
and then return that address back to the caller.
Note that in about 15% of cases (my experience metric) the geo location will be way off. The classic example is that most AOL users are routed through a small number of proxy servers. However, there are many other cases where the public IP does not match the user’s actual location. Additionally, Geo IP databases are sometimes just wrong.
Edit
It is not possible to detect your external IP address using only in-browser code.
The WebSocket has no provision to expose your external IP address.
https://www.rfc-editor.org/rfc/rfc6455
You need an outside server to tell you what IP it sees.