Question

I am working on implementing UpNP on C++, and I need to get the local internal IP address assigned by the router to make the sockets works. The address I need is the one that appears on routers where it shows the computers connected to the router and the local IP assigned to each computer. I am using this:

PHOSTENT      Addr    = NULL;
char          Host[MAX_PATH];

if( gethostname(Host, sizeof(Host)) == 0 )
{
    Address = gethostbyname( Host );
    if( Address != NULL )
    {
        //*(struct in_addr *)Address->h_addr_list[0]) <- this is my address
    }
}

This works fine on the computer I am testing, but that computer has only one network card, so I was wondering if maybe when a computer has more than one card or network device, Address->h_addr_list[0] may not be the one I need and it could be in another index of that array.

Will [0] always retrieve the IP assigned by the router?

Answer 1

(Assuming winsock here, as per previous question)

You shouldn’t assume that the first address is the correct one (as there may be multiple interfaces, and more than one may be active)

I’d recommend enumerating addresses using either getaddrinfo with an empty pNodeName argument, or GetAdaptersAddresses.

Both of these return a linked lists with your system’s registered addresses