Linked List in C and getifaddrs() - c++

Question

I've a problem with linked list. I'm using getifaddrs() to get ifaces info in Linux.
At first, i created an struct for save the interfaces infos.
This is a struct:
typedef struct iface {
char * interface_name;
char * interface_addr_ipv4;
char * interface_addr_ipv6;
char * interface_netmask;
char * interface_broadcast;
char * interface_mac_addr;
int interface_active;
struct iface * next_interface;
} Interface;
After this, i identify all ifaces of system in this way, even if they are not configured with an IP:
if (getifaddrs(&ifaddr) == -1)
return GET_INFO_IFACES_FAILED;
struct iface * iface_aux;
struct ifaddrs * ifaddr_aux;
struct sockaddr_in * ip;
iface_aux = iface;
for (ifaddr_aux=ifaddr;ifaddr_aux!=NULL;ifaddr_aux=ifaddr_aux->ifa_next) {
iface_aux->interface_name = ifaddr_aux->ifa_name;
if (ip->sin_family == AF_PACKET) {
get_interface_mac_addr(iface_aux);
iface_aux->interface_addr_ipv4 = NULL;
iface_aux->interface_addr_ipv6 = NULL;
iface_aux->next_interface = (Interface *) malloc(sizeof (Interface));
iface_aux = iface_aux->next_interface;
iface_aux->next_interface = NULL;
}
}
After all this, i do other loop to get ip address of interfaces, this is the code:
iface_aux = iface; //go to the firts pointer
for (ifaddr_aux=ifaddr;ifaddr_aux!=NULL;ifaddr_aux=ifaddr_aux->ifa_next) {
ip = (struct sockaddr_in *) ifaddr_aux->ifa_addr;
if (ip->sin_family == AF_INET) {
get_interface_ifaddr(iface_aux, ip);
get_interface_netmask(iface_aux, ifaddr);
get_interface_broadcast(iface_aux, ifaddr);
iface_aux = iface_aux->next_interface;
}
}
The code of function get_interface_ifaddr is:
int get_interface_ifaddr(Interface * iface, struct sockaddr_in * ip) {
iface->interface_addr_ipv4 = inet_ntoa(ip->sin_addr);
if (iface->interface_addr_ipv4 == NULL)
return GET_IFADDR_FAILED;
return GET_IPADDR_SUCCESS;
}
The problem is, when i do another loop to see the interfaces infos, all nodes of the list, stay with the last ip:
for (iface_aux=iface;iface_aux->next_interface!=NULL;iface_aux=iface_aux->next_interface) {
printf("Interface Name: %s\n", iface_aux->interface_name);
printf("Interface IP: %s\n", iface_aux->interface_addr_ipv4);
}
The strange thing is that the name of the interfaces is correct, but when i get the address, all nodes of the list, are to the same address.
Someone know what is going on?
PS: i'm new in c and linked list.
Thanks for your atention.

Answer 1

inet_ntoa uses a same memory region to return result. You need to allocate interface_addr_ipv4 by yourself and to copy the data manually.
char *tmp = inet_ntoa(ip->sin_addr);
iface->interface_addr_ipv4 = malloc(sizeof(char) * (strlen(tmp) + 1)); /* Don't forget to free() */
strcpy(iface->interface_addr_ipv4, tmp);
From the docs:
inet_ntoa() returns the dots-and-numbers string in a static buffer that is overwritten with each call to the function.
Better way is just to use inet_ntop:
inet_ntop(AF_INET, ip->sin_addr,
iface->interface_addr_ipv4, sizeof(iface->interface_addr_ipv4));
Where iface->interface_addr_ipv4 is an char array:
char interface_addr_ipv4[INET_ADDRSTRLEN];