stringstreams problem

I'm looking to take an IP address (in the form aaa.bbb.ccc.ddd), which I've stored as a string (m_Address), and convert the octets into four integers (m_A, m_B, m_C, m_D). I parsed the string m_Address into four strings, each containing one of the octets (a_string, b_string, c_string, d_string) and am trying to use stringstreams to convert them to ints. The first conversion works (a_string to m_A), but the rest do not. Successive calls to istringstream::str() seem to fail. I'd rather not make four istringstream objects if I don't have to.

Also, is there perhaps an easier way to parse the initial string into the four octets? Thanks to all who help.

Code:

int ConvertStringToInt(string m_Address)
{
    //N.B. Code modified for posting purposes.
    //Error checking, etc. removed for space and clarity.


    //Returns 0 on success, 1 on error.
    
    int count = 0;
    string a_string = "";
    string b_string = "";
    string c_string = "";
    string d_string = "";
    int m_A, m_B, m_C, m_D;
    
    for(int i = 0; i < m_Address.length(); ++i)
    {
        if(isdigit(m_Address[i]))
        {
            if(count == 0)  //aaa
                a_string += m_Address[i];
            else
                if(count == 1)  //bbb
                    b_string += m_Address[i];
                else
                    if(count == 2)  //ccc
                        c_string += m_Address[i];
                    else
                        if(count == 3)  //ddd
                            d_string += m_Address[i];
        }
        else    //Not a digit.
            if(m_Address[i] == '.')
                ++count;
    }

    //Convert strings to integers.
    istringstream stream_buffer;
    stream_buffer.str(a_string);
    stream_buffer >> m_A;
    stream_buffer.str(b_string);
    stream_buffer >> m_B;
    stream_buffer.str(c_string);
    stream_buffer >> m_C;
    stream_buffer.str(d_string);
    stream_buffer >> m_D;

    /***What I'd like to avoid doing***/
    //m_A = atoi(a_string.c_str());
    //m_B = atoi(b_string.c_str());
    //m_C = atoi(c_string.c_str());
    //m_D = atoi(d_string.c_str());
    /****************************/

    return(0);  //Success!    
}

you have to clear() the string stream each time.

however there's a much easier way to do this!
if m_address is "192.168.0.1" (for example) you can simply read it directly out of the stringstream as follows

Code:

int oct1, oct2, oct3, oct4;
char dot;

string addr = "192.168.0.1";

stringstream str(addr);

str >> oct1 >> dot >> oct2 >> dot >> oct3 >> dot >> oct4;

easy as that.