#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string>
#include <iostream>

using std::string;
void netmaskToBitLength(string& mp2Ip4Mask)
{
        unsigned long int res = inet_addr(mp2Ip4Mask.c_str());   // 16777215
        int oneCnt = 0;
        while (res)
        {
                oneCnt += (res & 1);
                res >>= 1;
        }
        mp2Ip4Mask = std::to_string(oneCnt);
}

int main()
{
        string ip4 = string("255.255.255.0");
    unsigned long int res =  inet_addr(ip4.c_str());
        std::cout << res << std::endl;

        netmaskToBitLength(ip4);
        std::cout << "ip4 is : " << ip4 << std::endl;   //   ip4 is : 24
}