I’m trying to solve a bug in which I try to print the ip adress of my machine. The machine is using a redhat OS. The goal is to obtain the host id using gethostid(), and then use the function inet_ntoa to convert its value to a string.

The problem is that the result is showing the address in a wrong order. The ip has the following order a.b.c.d, but the result of inet_ntoa shows it like this b.a.d.c. I’m aware of the endianess issue when using these functions, but I thought that by not respecting the endianess the result was a reversed IP address

I think that the issue could be in the value returned by the gethostid(). But if this is the case then I’m not sure why it’s giving me a wrong id.

My ip adress is 172.30.223.27

gethostid() returns 514595807 which in hexadecimal is 1EAC1BDF, and then converted to bytes 30.172.27.223

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

int main() {
  long hostId = gethostid();
  std::cout << "Host ID: " << hostId << std::endl;

  struct in_addr addr = inet_makeaddr(hostId,0 );

  ::std::string ipv4_addr_str = inet_ntoa(addr);

  std::cout << "IP using inet_ntoa: " << ipv4_addr_str << std::endl;

  char ipString[INET_ADDRSTRLEN];
  inet_ntop(AF_INET, &addr, ipString, INET_ADDRSTRLEN);

  std::cout << "IP using using inet_ntop: " << ipString << std::endl;

  return 0;
}

And the output is:

Host ID: 514595807
IP using inet_ntoa: 30.172.27.223
IP using using inet_ntop: 30.172.27.223

I tried using inet_ntoa and inet_ntop to see if the issue is at the moment of printing the IP, but it seems that the problem is located in the value obtained by gethostid()

I hope you can explain to me why does this occur.

Thanks!