Question

How can I programmatically get the Internet IP address?

1) If the computer is directly connected to the Internet using a USB modem.

2) If the computer is connected to the internet via another computer or a modem/router.

I there a way to do both?

P.S. This link gives exactly the Internet IP, but how can I use it in my program?

Answer 1

1. You can write socket code to send an http request to that link.

2. Under unix/linux/cygwin you can use system(“wget http://www.whatismyip.com/automation/n09230945.asp“); then open the file “n09230945.asp” and read its contents.

Here is an example of how to make the request using sockets (I modified an online example for this specific purpose). NOTE: It is an example and a real implementation would need to handle the errors better:

#include <iostream>
#include <cstring>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>

#define RCVBUFSIZE 1024

int main(int argc, char *argv[])
{
    int sock;                        // Socket descriptor
    struct sockaddr_in servAddr;     // server address
    unsigned short servPort;         // server port
    char const *servIP;              // Server IP address (dotted quad)
    char const *request;             // String to send to server
    char recvBuffer[RCVBUFSIZE];     // Buffer for response string
    unsigned int requestLen;         // Length of string to send
    int bytesRcvd;                   // Bytes read in single recv()
    bool status = true;

    // Initialize port
    servIP = "72.233.89.199";
    servPort = 80;
    request = "GET /automation/n09230945.asp HTTP/1.1\r\nHost: www.whatismyip.com\r\n\r\n";

    std::cout << request << std::endl;

    /* Create a reliable, stream socket using TCP */
    if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
    {
        status = false;
    }

    if (status)
    {
        // Convert dotted decimal into binary server address.
        memset(&servAddr, 0, sizeof(servAddr));
        servAddr.sin_family      = AF_INET;
        servAddr.sin_addr.s_addr = inet_addr(servIP);
        servAddr.sin_port        = htons(servPort);

        // Connect to the server.
        if (connect(sock, (struct sockaddr *) &servAddr, sizeof(servAddr)) < 0)
        {
            status = false;
        }
    }

    if (status)
    {
        // Calculate request length.
        requestLen = strlen(request);

        // Send the request to the server.
        if (send(sock, request, requestLen, 0) != requestLen)
        {
            status = false;
        }
    }

    if (status)
    {
        std::cout << "My IP Address: ";

        if ((bytesRcvd = recv(sock, recvBuffer, RCVBUFSIZE - 1, 0)) <= 0)
        {
            status = false;
        }

        if (status && (bytesRcvd >0) && (bytesRcvd < (RCVBUFSIZE-1)))
        {
            recvBuffer[bytesRcvd] = '\0';
            std::cout << recvBuffer << std::endl;
        }
    }

    close(sock);

    return 0;
}