Question

On a Linux box, the common interface names look like eth0, eth1, etc. I know how to find at least one IP address using gethostbyname or similar functions, but I don’t know any way to specify which named interface I want the IP address of. I could use ifconfig and parse the output, but shelling out for this information seems… inelegant.

Is there a way to, say, enumerate all the interfaces and their IP addresses (and maybe MAC addresses) into a collection? Or at least something along the lines of gethostbyinterface('eth0')?

Answer 1

// Originally from http://www.tlug.org.za/wiki/index.php/Obtaining_your_own_IP_address  #include <sys/types.h> #include <sys/socket.h> #include <sys/ioctl.h> #include <net/if.h> #include <netinet/in.h> #include <arpa/inet.h> #include <string.h> #include <stdio.h> #include <unistd.h>  /**  * getIPv4()  *  * This function takes a network identifier such as 'eth0' or 'eth0:0' and  * a pointer to a buffer of at least 16 bytes and then stores the IP of that  * device gets stored in that buffer.  *  * it return 0 on success or -1 on failure.  *  * Author:  Jaco Kroon <[e-mail]>  */ int getIPv4(const char * dev, char * ipv4) {     struct ifreq ifc;     int res;     int sockfd = socket(AF_INET, SOCK_DGRAM, 0);      if(sockfd < 0)         return -1;     strcpy(ifc.ifr_name, dev);     res = ioctl(sockfd, SIOCGIFADDR, &ifc);     close(sockfd);     if(res < 0)         return -1;          strcpy(ipv4, inet_ntoa(((struct sockaddr_in*)&ifc.ifr_addr)->sin_addr));     return 0; }   int main() {     char ip[16];     if(getIPv4('eth0', ip) == 0)         printf('IPv4: %s\n', ip);     else         printf('No IP\n');     return 0;  } 

Update: Moved dead link to a comment (for posterity) (thanks @obayhan), and added syntax highlighting.