Problem
On Linux, how can I acquire the IPv4 address of an interface using C code?
For example, I’d like to know what IP address eth0 has (if any).
Asked by leeeroy
Solution #1
Try this:
#include <stdio.h>
#include <unistd.h>
#include <string.h> /* for strncpy */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>
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, &ifr);
close(fd);
/* display result */
printf("%s\n", inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr));
return 0;
}
This is where the code sample came from.
Answered by Filip Ekberg
Solution #2
You can use getifaddrs in addition to the ioctl() approach Filip provided (). A sample program can be seen at the bottom of the man page.
Answered by Duck
Solution #3
Try this code, which utilizes getifaddrs(), if you’re seeking for an address (IPv4) of a specific interface, such as wlan0:
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char *argv[])
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NI_MAXHOST];
if (getifaddrs(&ifaddr) == -1)
{
perror("getifaddrs");
exit(EXIT_FAILURE);
}
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
{
if (ifa->ifa_addr == NULL)
continue;
s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if((strcmp(ifa->ifa_name,"wlan0")==0)&&(ifa->ifa_addr->sa_family==AF_INET))
{
if (s != 0)
{
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\tInterface : <%s>\n",ifa->ifa_name );
printf("\t Address : <%s>\n", host);
}
}
freeifaddrs(ifaddr);
exit(EXIT_SUCCESS);
}
You can use eth0 for ethernet and lo for local loopback instead of wlan0.
The structure of the data structures employed, as well as thorough explanations, can be found here.
This website will be a fantastic place to start if you want to learn more about linked lists in C.
Answered by sjsam
Solution #4
My two cents: the same code works on both iOS and Android.
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#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(&ifaddr) == -1)
{
perror("getifaddrs");
exit(EXIT_FAILURE);
}
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next)
{
if (ifa->ifa_addr == NULL)
continue;
s=getnameinfo(ifa->ifa_addr,sizeof(struct sockaddr_in),host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if( /*(strcmp(ifa->ifa_name,"wlan0")==0)&&( */ ifa->ifa_addr->sa_family==AF_INET) // )
{
if (s != 0)
{
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\tInterface : <%s>\n",ifa->ifa_name );
printf("\t Address : <%s>\n", host);
}
}
freeifaddrs(ifaddr);
}
@end
To view data, I just removed the test against wlan0. ps “Family” can be removed.
Answered by ingconti
Solution #5
I recently had the similar problem, and here is the code I came up with, which works. Make certain you use the network interface’s name precisely as you have it (could be “eth0” or else).
To acquire the interface name and utilize it in C, you must first check if ifconfigcommand is available.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <unistd.h>
#include <linux/if.h>
#include <errno.h>
#include <ifaddrs.h>
#include <netinet/in.h>
#include <arpa/inet.h>
void extract_ipaddress()
{
//create an ifreq struct for passing data in and out of ioctl
struct ifreq my_struct;
//declare and define the variable containing the name of the interface
char *interface_name="enp0s3"; //a very frequent interface name is "eth0";
//the ifreq structure should initially contains the name of the interface to be queried. Which should be copied into the ifr_name field.
//Since this is a fixed length buffer, one should ensure that the name does not cause an overrun
size_t interface_name_len=strlen(interface_name);
if(interface_name_len<sizeof(my_struct.ifr_name))
{
memcpy(my_struct.ifr_name,interface_name,interface_name_len);
my_struct.ifr_name[interface_name_len]=0;
}
else
{
perror("Copy name of interface to ifreq struct");
printf("The name you provided for the interface is too long...\n");
}
//provide an open socket descriptor with the address family AF_INET
/* ***************************************************************
* All ioctl call needs a file descriptor to act on. In the case of SIOCGIFADDR this must refer to a socket file descriptor. This socket must be in the address family that you wish to obtain (AF_INET for IPv4)
* ***************************************************************
*/
int file_descriptor=socket(AF_INET, SOCK_DGRAM,0);
if(file_descriptor==-1)
{
perror("Socket file descriptor");
printf("The construction of the socket file descriptor was unsuccessful.\n");
return -1;
}
//invoke ioctl() because the socket file descriptor exists and also the struct 'ifreq' exists
int myioctl_call=ioctl(file_descriptor,SIOCGIFADDR,&my_struct);
if (myioctl_call==-1)
{
perror("ioctl");
printf("Ooops, error when invoking ioctl() system call.\n");
close(file_descriptor);
return -1;
}
close(file_descriptor);
/* **********************************************************************
* If this completes without error , then the hardware address of the interface should have been returned in the 'my_struct.ifr_addr' which is types as struct sockaddr_in.
* ***********************************************************************/
//extract the IP Address (IPv4) from the my_struct.ifr_addr which has the type 'ifreq'
/* *** Cast the returned address to a struct 'sockaddr_in' *** */
struct sockaddr_in * ipaddress= (struct sockaddr_in *)&my_struct.ifr_addr;
/* *** Extract the 'sin_addr' field from the data type (struct) to obtain a struct 'in_addr' *** */
printf("IP Address is %s.\n", inet_ntoa(ipaddress->sin_addr));
}
Answered by George
Post is based on https://stackoverflow.com/questions/2283494/get-ip-address-of-an-interface-on-linux