Determine whether or not a TCP/IP port is already in use under Windows?

Question

The cross platform dev environment I use has a built in function that is supposed to indicate whether or not a tcp port is available. However, the function malfunctions under Vista and always returns "available".

Is there an easy way, such as a dll function, I can use to correctly determine this information without needing .Net?

Answer 1

You can attempt to bind to and listen on the port using the usual Winsock functions. If something else is already listening on the same port, you will get an error (WSAEADDRINUSE from bind()).

Answer 2

To avoid bringing in added dependencies or windows-specific code you could simply try to use the port and catch any problems (such as interception by firewall software).

Answer 3

Simply use Win32 Nw apis to enumerate TCP ports.