Function ip_to_hostname

dlib/sockets/sockets_kernel_1.cpp:187–230

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

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

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

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

            hostent* address;
            unsigned long ipnum = inet_addr(ip.c_str());

            // if inet_addr couldn't convert ip then return an error
            if (ipnum == INADDR_NONE)
            {
                return OTHER_ERROR;
            }
            address = gethostbyaddr(reinterpret_cast<char*>(&ipnum),4,AF_INET);

            // check if gethostbyaddr returned an error
            if (address == 0)
            {
                return OTHER_ERROR;
            }
            hostname.assign(address->h_name);

        }
        catch (...)
        {
            return OTHER_ERROR;
        }
        return 0;

    }

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