Home ยป Get the IP Address of local computer

Get the IP Address of local computer

Solutons:


The question is trickier than it appears, because in many cases there isn’t “an IP address for the local computer” so much as a number of different IP addresses. For example, the Mac I’m typing on right now (which is a pretty basic, standard Mac setup) has the following IP addresses associated with it:

fe80::1%lo0  
127.0.0.1 
::1 
fe80::21f:5bff:fe3f:1b36%en1 
10.0.0.138 
172.16.175.1
192.168.27.1

… and it’s not just a matter of figuring out which of the above is “the real IP address”, either… they are all “real” and useful; some more useful than others depending on what you are going to use the addresses for.

In my experience often the best way to get “an IP address” for your local computer is not to query the local computer at all, but rather to ask the computer your program is talking to what it sees your computer’s IP address as. e.g. if you are writing a client program, send a message to the server asking the server to send back as data the IP address that your request came from. That way you will know what the relevant IP address is, given the context of the computer you are communicating with.

That said, that trick may not be appropriate for some purposes (e.g. when you’re not communicating with a particular computer) so sometimes you just need to gather the list of all the IP addresses associated with your machine. The best way to do that under Unix/Mac (AFAIK) is by calling getifaddrs() and iterating over the results. Under Windows, try GetAdaptersAddresses() to get similar functionality. For example usages of both, see the GetNetworkInterfaceInfos() function in this file.

The problem with all the approaches based on gethostbyname is that you will not get all IP addresses assigned to a particular machine. Servers usually have more than one adapter.

Here is an example of how you can iterate through all Ipv4 and Ipv6 addresses on the host machine:

void ListIpAddresses(IpAddresses& ipAddrs)
{
  IP_ADAPTER_ADDRESSES* adapter_addresses(NULL);
  IP_ADAPTER_ADDRESSES* adapter(NULL);

  // Start with a 16 KB buffer and resize if needed -
  // multiple attempts in case interfaces change while
  // we are in the middle of querying them.
  DWORD adapter_addresses_buffer_size = 16 * KB;
  for (int attempts = 0; attempts != 3; ++attempts)
  {
    adapter_addresses = (IP_ADAPTER_ADDRESSES*)malloc(adapter_addresses_buffer_size);
    assert(adapter_addresses);

    DWORD error = ::GetAdaptersAddresses(
      AF_UNSPEC, 
      GAA_FLAG_SKIP_ANYCAST | 
        GAA_FLAG_SKIP_MULTICAST | 
        GAA_FLAG_SKIP_DNS_SERVER |
        GAA_FLAG_SKIP_FRIENDLY_NAME, 
      NULL, 
      adapter_addresses,
      &adapter_addresses_buffer_size);

    if (ERROR_SUCCESS == error)
    {
      // We're done here, people!
      break;
    }
    else if (ERROR_BUFFER_OVERFLOW == error)
    {
      // Try again with the new size
      free(adapter_addresses);
      adapter_addresses = NULL;

      continue;
    }
    else
    {
      // Unexpected error code - log and throw
      free(adapter_addresses);
      adapter_addresses = NULL;

      // @todo
      LOG_AND_THROW_HERE();
    }
  }

  // Iterate through all of the adapters
  for (adapter = adapter_addresses; NULL != adapter; adapter = adapter->Next)
  {
    // Skip loopback adapters
    if (IF_TYPE_SOFTWARE_LOOPBACK == adapter->IfType)
    {
      continue;
    }

    // Parse all IPv4 and IPv6 addresses
    for (
      IP_ADAPTER_UNICAST_ADDRESS* address = adapter->FirstUnicastAddress; 
      NULL != address;
      address = address->Next)
    {
      auto family = address->Address.lpSockaddr->sa_family;
      if (AF_INET == family)
      {
        // IPv4
        SOCKADDR_IN* ipv4 = reinterpret_cast<SOCKADDR_IN*>(address->Address.lpSockaddr);

        char str_buffer[INET_ADDRSTRLEN] = {0};
        inet_ntop(AF_INET, &(ipv4->sin_addr), str_buffer, INET_ADDRSTRLEN);
        ipAddrs.mIpv4.push_back(str_buffer);
      }
      else if (AF_INET6 == family)
      {
        // IPv6
        SOCKADDR_IN6* ipv6 = reinterpret_cast<SOCKADDR_IN6*>(address->Address.lpSockaddr);

        char str_buffer[INET6_ADDRSTRLEN] = {0};
        inet_ntop(AF_INET6, &(ipv6->sin6_addr), str_buffer, INET6_ADDRSTRLEN);

        std::string ipv6_str(str_buffer);

        // Detect and skip non-external addresses
        bool is_link_local(false);
        bool is_special_use(false);

        if (0 == ipv6_str.find("fe"))
        {
          char c = ipv6_str[2];
          if (c == '8' || c == '9' || c == 'a' || c == 'b')
          {
            is_link_local = true;
          }
        }
        else if (0 == ipv6_str.find("2001:0:"))
        {
          is_special_use = true;
        }

        if (! (is_link_local || is_special_use))
        {
          ipAddrs.mIpv6.push_back(ipv6_str);
        }
      }
      else
      {
        // Skip all other types of addresses
        continue;
      }
    }
  }

  // Cleanup
  free(adapter_addresses);
  adapter_addresses = NULL;

  // Cheers!
}

You can use gethostname followed by gethostbyname to get your local interface internal IP.

This returned IP may be different from your external IP though. To get your external IP you would have to communicate with an external server that will tell you what your external IP is. Because the external IP is not yours but it is your routers.

//Example: b1 == 192, b2 == 168, b3 == 0, b4 == 100
struct IPv4
{
    unsigned char b1, b2, b3, b4;
};

bool getMyIP(IPv4 & myIP)
{
    char szBuffer[1024];

    #ifdef WIN32
    WSADATA wsaData;
    WORD wVersionRequested = MAKEWORD(2, 0);
    if(::WSAStartup(wVersionRequested, &wsaData) != 0)
        return false;
    #endif


    if(gethostname(szBuffer, sizeof(szBuffer)) == SOCKET_ERROR)
    {
      #ifdef WIN32
      WSACleanup();
      #endif
      return false;
    }

    struct hostent *host = gethostbyname(szBuffer);
    if(host == NULL)
    {
      #ifdef WIN32
      WSACleanup();
      #endif
      return false;
    }

    //Obtain the computer's IP
    myIP.b1 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b1;
    myIP.b2 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b2;
    myIP.b3 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b3;
    myIP.b4 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b4;

    #ifdef WIN32
    WSACleanup();
    #endif
    return true;
}

You can also always just use 127.0.0.1 which represents the local machine always.

Subnet mask in Windows:

You can get the subnet mask (and gateway and other info) by querying subkeys of this registry entry:

HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParametersInterfaces

Look for the registry value SubnetMask.

Other methods to get interface information in Windows:

You could also retrieve the information you’re looking for by using:
WSAIoctl with this option: SIO_GET_INTERFACE_LIST

Related Solutions

When should I not kill -9 a process?

Generally, you should use kill (short for kill -s TERM, or on most systems kill -15) before kill -9 (kill -s KILL) to give the target process a chance to clean up after itself. (Processes can't catch or ignore SIGKILL, but they can and often do catch SIGTERM.)...

Default value for UUID column in Postgres

tl;dr Call DEFAULT when defining a column to invoke one of the OSSP uuid functions. The Postgres server will automatically invoke the function every time a row is inserted. CREATE TABLE tbl ( pkey UUID NOT NULL DEFAULT uuid_generate_v1() , CONSTRAINT pkey_tbl...

comparing five integers with if , else if statement

try this : int main () { int n1, n2, n3, n4, n5, biggest,smallest; cout << "Enter the five numbers: "; cin >> n1 >> n2 >> n3 >> n4 >> n5 ; smallest=biggest=n1; if(n2>biggest){ biggest=n2; } if(n2<smallest){ smallest=n2;...

How to play YouTube audio in background/minimised?

Here's a solution using entirely free and open source software. The basic idea is that although YouTube can't play clips in the background, VLC for Android can play clips in the background, so all we need to do is pipe the clip to VLC where we can listen to it...

Why not use “which”? What to use then?

Here is all you never thought you would ever not want to know about it: Summary To get the pathname of an executable in a Bourne-like shell script (there are a few caveats; see below): ls=$(command -v ls) To find out if a given command exists: if command -v...

Split string into Array of Arrays [closed]

If I got correct what you want to receive as a result, then this code would make what you want: extension Array { func chunked(into size: Int) -> [[Element]] { return stride(from: 0, to: self.count, by: size).map { Array(self[$0 ..< Swift.min($0 + size,...

Retrieving n rows per group

Let's start with the basic scenario. If I want to get some number of rows out of a table, I have two main options: ranking functions; or TOP. First, let's consider the whole set from Production.TransactionHistory for a particular ProductID: SELECT...

Don’t understand how my mum’s Gmail account was hacked

IMPORTANT: this is based on data I got from your link, but the server might implement some protection. For example, once it has sent its "silver bullet" against a victim, it might answer with a faked "silver bullet" to the same request, so that anyone...

What is /storage/emulated/0/?

/storage/emulated/0/Download is the actual path to the files. /sdcard/Download is a symlink to the actual path of /storage/emulated/0/Download However, the actual files are located in the filesystem in /data/media, which is then mounted to /storage/emulated/0...

How can I pass a command line argument into a shell script?

The shell command and any arguments to that command appear as numbered shell variables: $0 has the string value of the command itself, something like script, ./script, /home/user/bin/script or whatever. Any arguments appear as "$1", "$2", "$3" and so on. The...

What is pointer to string in C?

argv is an array of pointers pointing to zero terminated c-strings. I painted the following pretty picture to help you visualize something about the pointers. And here is a code example that shows you how an operating system would pass arguments to your...

How do mobile carriers know video resolution over HTTPS connections?

This is an active area of research. I happen to have done some work in this area, so I'll share what I can about the basic idea (this work was with industry partners and I can't share the secret details ๐Ÿ™‚ ). The tl;dr is that it's often possible to identify an...

How do I change the name of my Android device?

To change the hostname (device name) you have to use the terminal (as root): For Eclair (2.1): echo MYNAME > /proc/sys/kernel/hostname For Froyo (2.2): (works also on most 2.3) setprop net.hostname MYNAME Then restart your wi-fi. To see the change, type...

How does reverse SSH tunneling work?

I love explaining this kind of thing through visualization. ๐Ÿ™‚ Think of your SSH connections as tubes. Big tubes. Normally, you'll reach through these tubes to run a shell on a remote computer. The shell runs in a virtual terminal (tty). But you know this part...

Difference between database vs user vs schema

In Oracle, users and schemas are essentially the same thing. You can consider that a user is the account you use to connect to a database, and a schema is the set of objects (tables, views, etc.) that belong to that account. See this post on Stack Overflow:...