Function hostname_to_ip

dlib/sockets/sockets_kernel_1.cpp:127–183

// -----------------

    int 
    hostname_to_ip (
        const std::string& hostname,
        std::string& ip,
        int n
    )
    {
        // ensure that WSAStartup has been called and WSACleanup will eventually 
        // be called when program ends
        sockets_startup();

        try 
        {
            // lock this mutex since gethostbyname isn't really thread safe
            auto_mutex M(sockets_kernel_1_mutex::startup_lock);

            // if no hostname was given then return error
            if ( hostname.empty())
                return OTHER_ERROR;

            hostent* address;
            address = gethostbyname(hostname.c_str());
            
            if (address == 0)
            {
                return OTHER_ERROR;
            }

            // find the nth address
            in_addr* addr = reinterpret_cast<in_addr*>(address->h_addr_list[0]);
            for (int i = 1; i <= n; ++i)
            {
                addr = reinterpret_cast<in_addr*>(address->h_addr_list[i]);

                // if there is no nth address then return error
                if (addr == 0)
                    return OTHER_ERROR;
            }

            char* resolved_ip = inet_ntoa(*addr);

            // check if inet_ntoa returned an error
            if (resolved_ip == NULL)
            {
                return OTHER_ERROR;
            }

            ip.assign(resolved_ip);

        }
        catch(...)
        {
            return OTHER_ERROR;
        }

        return 0;
    }