Get IP address of an interface on Linux

Question

How can I get the IPv4 address of an interface on Linux from C code   For example  I d like to get the IP address  if any  assigned to eth0

User · Answer

My 2 cents  the same code works even if iOS    include  lt arpa inet h gt   include  lt sys socket h gt   include  lt netdb h gt   include  lt ifaddrs h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt unistd h gt   include  lt string h gt      import  ViewController h    interface ViewController      end   implementation ViewController  -  void viewDidLoad        super viewDidLoad          Do any additional setup after loading the view  typically from a nib      showIP         void showIP         struct ifaddrs  ifaddr   ifa      int family  s      char host NI MAXHOST        if  getifaddrs  amp ifaddr     -1                perror  getifaddrs            exit EXIT FAILURE               for  ifa   ifaddr  ifa    NULL  ifa   ifa- gt ifa next                if  ifa- gt ifa addr    NULL              continue           s getnameinfo ifa- gt ifa addr sizeof struct sockaddr in  host  NI MAXHOST  NULL  0  NI NUMERICHOST            if     strcmp ifa- gt ifa name  wlan0    0  amp  amp      ifa- gt ifa addr- gt sa family  AF INET                             if  s    0                                printf  getnameinfo   failed   s n   gai strerror s                    exit EXIT FAILURE                             printf   tInterface    lt  s gt  n  ifa- gt ifa name                printf   t  Address    lt  s gt  n   host                        freeifaddrs ifaddr        end   I simply removed the test against wlan0 to see data  ps You can remove  family

User · Answer

If you don t mind the binary size  you can use iproute2 as library   iproute2-as-lib  Pros    No need to write the socket layer code   More or even more information about network interfaces can be got  Same functionality with the iproute2 tools  Simple API interface    Cons    iproute2-as-lib library size is big   500kb

User · Answer

If you re looking for an address  IPv4  of the specific interface say wlan0 then try this code which uses getifaddrs      include  lt arpa inet h gt   include  lt sys socket h gt   include  lt netdb h gt   include  lt ifaddrs h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt unistd h gt   include  lt string h gt  int main int argc  char  argv          struct ifaddrs  ifaddr   ifa      int family  s      char host NI MAXHOST        if  getifaddrs  amp ifaddr     -1                 perror  getifaddrs            exit EXIT FAILURE               for  ifa   ifaddr  ifa    NULL  ifa   ifa- gt ifa next                 if  ifa- gt ifa addr    NULL              continue             s getnameinfo ifa- gt ifa addr sizeof struct sockaddr in  host  NI MAXHOST  NULL  0  NI NUMERICHOST            if  strcmp ifa- gt ifa name  wlan0    0  amp  amp  ifa- gt ifa addr- gt sa family  AF INET                         if  s    0                                printf  getnameinfo   failed   s n   gai strerror s                    exit EXIT FAILURE                             printf   tInterface    lt  s gt  n  ifa- gt ifa name                printf   t  Address    lt  s gt  n   host                         freeifaddrs ifaddr       exit EXIT SUCCESS       You can replace wlan0 with eth0 for ethernet and lo for local loopback   The structure and detailed explanations of the data structures used could be found here   To  know more about linked list in C this page will be a good starting point

User · Answer

In addition to the ioctl   method Filip demonstrated you can use getifaddrs     There is an example program at the bottom of the man page

User · Answer

Try this    include  lt stdio h gt   include  lt unistd h gt   include  lt string h gt     for strncpy      include  lt sys types h gt   include  lt sys socket h gt   include  lt sys ioctl h gt   include  lt netinet in h gt   include  lt net if h gt   include  lt arpa inet h gt   int main      int fd   struct ifreq ifr    fd   socket AF INET  SOCK DGRAM  0        I want to get an IPv4 IP address     ifr ifr addr sa family   AF INET       I want IP address attached to  eth0      strncpy ifr ifr name   eth0   IFNAMSIZ-1     ioctl fd  SIOCGIFADDR   amp ifr     close fd        display result     printf   s n   inet ntoa   struct sockaddr in    amp ifr ifr addr - gt sin addr      return 0      The code sample is taken from here

[c] Get IP address of an interface on Linux

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