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I am build my own function to aquire the local ip address and together using another function provided from this site Get the IP Address of local computer

I am using a 16-length character array, and this is the return value of during progress, 192.168.056.001Íýýýý ,it should be like"192.168.056.001" and a '\0' ,something must be wrong here, just can't figure out.And this cause problems when I sending it through the ethernet by creating UDP packets.

    char* YourApplication::GetMyIP() {
    char* IPAdd = new char[16];
    if (YourApplication::GenerateIP(MyIP)) {
        int b1 = MyIP.b1;
        int hundreds,tens;
        if (b1 < 100) {
            IPAdd[0] = '0';
            if (b1 < 10) {
                IPAdd[1] = '0';
                IPAdd[2] = b1 + 48;
            }
            else {
                tens = b1 / 10;
                IPAdd[1] = tens + 48;
                IPAdd[2] = b1 % 10 + 48;
            }
        }
        else {
            hundreds = b1 / 100;
            IPAdd[0] = hundreds+48;
            tens = (b1 - 100*hundreds) / 10;
            IPAdd[1] = tens+48;
            IPAdd[2] = (b1 - 100 * hundreds - 10 * tens) + 48;
        }
        IPAdd[3] = '.';
        int b2 = MyIP.b2;
        if (b2 < 100) {
            IPAdd[4] = '0';
            if (b2 < 10) {
                IPAdd[5] = '0';
                IPAdd[6] = b2 + 48;
            }
            else {
                tens = b2 / 10;
                IPAdd[5] = tens + 48;
                IPAdd[6] = b2 % 10 + 48;
            }
        }
        else {
            hundreds = b2 / 100;
            IPAdd[4] = hundreds + 48;
            tens = (b2 - 100 * hundreds) / 10;
            IPAdd[5] = tens + 48;
            IPAdd[6] = (b2 - 100 * hundreds - 10 * tens) + 48;
        }
        IPAdd[7] = '.';
        int b3 = MyIP.b3;
        if (b3 < 100) {
            IPAdd[8] = '0';
            if (b3 < 10) {
                IPAdd[9] = '0';
                IPAdd[10] = b3 + 48;
            }
            else {
                tens = b3 / 10;
                IPAdd[9] = tens + 48;
                IPAdd[10] = b3 % 10 + 48;
            }
        }
        else {
            hundreds = b3 / 100;
            IPAdd[8] = hundreds + 48;
            tens = (b3 - 100 * hundreds) / 10;
            IPAdd[9] = tens + 48;
            IPAdd[10] = (b3 - 100 * hundreds - 10 * tens) + 48;
        }
        IPAdd[11] = '.';
        int b4 = MyIP.b4;
        if (b4 < 100) {
            IPAdd[12] = '0';
            if (b4 < 10) {
                IPAdd[13] = '0';
                IPAdd[14] = b4 + 48;
            }
            else {
                tens = b4 / 10;
                IPAdd[13] = tens + 48;
                IPAdd[14] = b4 % 10 + 48;
            }
        }
        else {
            hundreds = b4 / 100;
            IPAdd[12] = hundreds + 48;
            tens = (b4 - 100 * hundreds) / 10;
            IPAdd[13] = tens + 48;
            IPAdd[14] = (b4 - 100 * hundreds - 10 * tens) + 48;
        }
    }
    return  IPAdd;
}

And below is that function from that site:

bool YourApplication::GenerateIP(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;
}
Community
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Leslie Lee
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    C is not C++. Use a debugger or provide a [MCVE]. – Vittorio Romeo Mar 06 '17 at 17:09
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    I think you have an off-by-one issue `char* IPAdd = new char[16];` should be `char* IPAdd = new char[16 + 1];` to account for `'\0'` – Ingenioushax Mar 06 '17 at 17:10
  • I just wondered I assigned each element individually and manually, why there are chars like "Íýýýý"? And due the NDA，I cant give details about other parts, and its also unrelevant to this function, sorry for that. I only give the array 15 elements ,the 16th is left for the \0. – Leslie Lee Mar 06 '17 at 17:20
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    S_un.S_un_b.s_b2? Say what? Use inet_ntop(). By the way you don't normally need a local IP address. – n. m. could be an AI Mar 06 '17 at 17:24

1 Answers1

1

Using libraries that manipulates byte strings (such as std::string) would automatically add a terminating character at the end of the array. However, since you're setting all the values yourself, you should set IPAddr[15] = '\0'.

AlexG
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  • Thx, I'll add the '\0' myself. As we are using a code based engine here, I have to use char type string to be consistent with other parts, and I havent tried send a packet with string before. – Leslie Lee Mar 06 '17 at 17:59