getifaddrs()--Return All Interface Addresses

  #include <ifaddrs.h>

  int getifaddrs(struct ifaddrs **ifap)

The getifaddrs() function stores a reference to a linked list of ifaddrs structures, one structure per interface. The end of the linked list of structures is indicated by a structure with an ifa_next of NULL.

Parameters

ifap

(I/O) Reference to the pointer to the linked list of network interface structures that contain the following:

• The pointer to the next structure
  
  
• The interface name
  
  
• The interface flags
  
  
• The interface address
  
  
• The interface netmask
  
  
• The broadcast address or the address of the other end of the link
  
  
• The pointer to the address specific data
  
  

The structure pointed to by the ifap parameter is defined in <ifaddrs.h>.

      struct ifaddrs
      {
        struct ifaddrs   *ifa_next;
        char             *ifa_name;
        u_int             ifa_flags;
        struct sockaddr  *ifa_addr;
        struct sockaddr  *ifa_netmask;
        union
        {
          struct sockaddr *ifu_broadaddr;
          struct sockaddr *ifu_dstaddr;
        }  ifa_ifu;
        void             *ifa_data;
      };

The ifa_next field contains a pointer to the next structure on the list. This field is NULL in the last structure on the list.

The ifa_name field contains the interface (line description) name.

The ifa_flags field contains flags that give some information about the interface.

The ifa_addr field references either the address of the interface or the link level address of the interface, if one exists; otherwise, it is NULL. (The sa_family field of the ifa_addr field should be consulted to determine the format of the ifa_addr address.)

The ifa_netmask field references the netmask associated with ifa_addr, if one is set; otherwise, it is NULL.

The ifa_ifu field is a union of the following:

• ifu_broadaddr, which should only be referenced for a non point-to-point interface, references the broadcast address associated with ifa_addr, if one exists; otherwise, it is NULL.
• ifu_dstaddr references the destination address on a point-to-point interface, if one exists; otherwise, it is NULL.

The ifa_data field is not used.

Authorities

No authorization is required.

Return Value

getifaddrs() returns an integer. Possible values are:

• -1 (unsuccessful)
  
  
• 0 (successful)

Error Conditions

When getifaddrs() fails, errno can be set to one of the following:

Usage Notes

1. The interface (line description) name stored at ifa_name will be returned in the default coded character set identifier (CCSID) currently in effect for the job.
2. For more information about the flags returned in ifa_flags, see <net/if.h>.
3. A variant of sockaddr structure will be used for ifa_addr, ifa_netmask, ifa_broadaddr, and ifa_dstaddr. The sockaddr_in structure will be used for AF_INET addresses and sockaddr_in6 will be used for AF_INET6 addresses.
4. The data returned by getifaddrs() is dynamically allocated and should be freed with freeifaddrs() when no longer needed.

Related Information

• freeifaddrs()--Free Dynamic Memory Allocated by getifaddrs()

Example

The following example shows how getifaddrs() is used.

Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <net/if.h>
#include <ifaddrs.h>
#include <errno.h>
#include <stdio.h>

int main()
{
  struct ifaddrs *interfaceArray = NULL, *tempIfAddr = NULL;
  void *tempAddrPtr = NULL;
  int rc = 0;
  char addressOutputBuffer[INET6_ADDRSTRLEN];
  
  rc = getifaddrs(&interfaceArray);  /* retrieve the current interfaces */
  if (rc == 0)
  {    
    for(tempIfAddr = interfaceArray; tempIfAddr != NULL; tempIfAddr = tempIfAddr->ifa_next)
    {
      if(tempIfAddr->ifa_addr->sa_family == AF_INET)
        tempAddrPtr = &((struct sockaddr_in *)tempIfAddr->ifa_addr)->sin_addr;
      else
        tempAddrPtr = &((struct sockaddr_in6 *)tempIfAddr->ifa_addr)->sin6_addr;
      
      printf("Internet Address:  %s \n",
             inet_ntop(tempIfAddr->ifa_addr->sa_family,
                       tempAddrPtr,
                       addressOutputBuffer,
                       sizeof(addressOutputBuffer)));

      printf("LineDescription :  %s \n", tempIfAddr->ifa_name);
      if(tempIfAddr->ifa_netmask != NULL)
      {
        if(tempIfAddr->ifa_netmask->sa_family == AF_INET)
          tempAddrPtr = &((struct sockaddr_in *)tempIfAddr->ifa_netmask)->sin_addr;
        else
          tempAddrPtr = &((struct sockaddr_in6 *)tempIfAddr->ifa_netmask)->sin6_addr;

        printf("Netmask         :  %s \n",
               inet_ntop(tempIfAddr->ifa_netmask->sa_family,
                         tempAddrPtr,
                         addressOutputBuffer,
                         sizeof(addressOutputBuffer)));
      }
      if(tempIfAddr->ifa_ifu.ifu_broadaddr != NULL)
      {
        /* If the ifa_flags field indicates that this is a P2P interface */
        if(tempIfAddr->ifa_flags & IFF_POINTOPOINT)
        {
          printf("Destination Addr:  ");
          if(tempIfAddr->ifa_ifu.ifu_dstaddr->sa_family == AF_INET)
            tempAddrPtr = &((struct sockaddr_in *)tempIfAddr->ifa_ifu.ifu_dstaddr)->sin_addr;
          else
            tempAddrPtr = &((struct sockaddr_in6 *)tempIfAddr->ifa_ifu.ifu_dstaddr)->sin6_addr;
        }
        else
        {
          printf("Broadcast Addr  :  ");
          if(tempIfAddr->ifa_ifu.ifu_broadaddr->sa_family == AF_INET)
            tempAddrPtr = &((struct sockaddr_in *)tempIfAddr->ifa_ifu.ifu_broadaddr)->sin_addr;
          else
            tempAddrPtr = &((struct sockaddr_in6 *)tempIfAddr->ifa_ifu.ifu_broadaddr)->sin6_addr;
        }
          
        printf("%s \n",
               inet_ntop(tempIfAddr->ifa_ifu.ifu_broadaddr->sa_family,
                         tempAddrPtr,
                         addressOutputBuffer,
                         sizeof(addressOutputBuffer)));
      }
      printf("\n");
    }

    freeifaddrs(interfaceArray);             /* free the dynamic memory */
    interfaceArray = NULL;                   /* prevent use after free  */
  }
  else
  {
     printf("getifaddrs() failed with errno =  %d %s \n",
            errno, strerror(errno));
     return rc;
  }
}

Output:

Assume the system has the following three interfaces configured:

• 9.5.139.105 (ETHVLINE)
• 127.0.0.1 (*LOOPBACK)
• ::1 (*LOOPBACK)

    Internet Address:  9.5.139.105
    LineDescription :  ETHVLINE
    Netmask         :  255.255.255.224
    Broadcast Addr  :  9.5.139.127

    Internet Address:  127.0.0.1
    LineDescription :  *LOOPBACK
    Netmask         :  255.0.0.0

    Internet Address:  ::1
    LineDescription :  *LOOPBACK
    Netmask         :  FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF

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