WinPcap 4.1.3

Typically, the first thing that a WinPcap-based application does is get a list of attached network adapters. Both libpcap and WinPcap provide the pcap_findalldevs_ex() function for this purpose: this function returns a linked list of pcap_if structures, each of which contains comprehensive information about an attached adapter. In particular, the fields name and description contain the name and a human readable description, respectively, of the corresponding device.

The following code retrieves the adapter list and shows it on the screen, printing an error if no adapters are found.

#include "pcap.h"
main()
{
pcap_if_t *alldevs;
int i=0;
char errbuf[PCAP_ERRBUF_SIZE];
/* Retrieve the device list from the local machine */
if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL /* auth is not needed */, &alldevs, errbuf) == -1)
{
fprintf(stderr,"Error in pcap_findalldevs_ex: %s\n", errbuf);
exit(1);
}
/* Print the list */
for(d= alldevs; d != NULL; d= d->next)
{
printf("%d. %s", ++i, d->name);
if (d->description)
printf(" (%s)\n", d->description);
else
printf(" (No description available)\n");
}
if (i == 0)
{
printf("\nNo interfaces found! Make sure WinPcap is installed.\n");
return;
}
/* We don't need any more the device list. Free it */
pcap_freealldevs(alldevs);
}
#define PCAP_SRC_IF_STRING
String that will be used to determine the type of source in use (file, remote/local interface).
Definition remote-ext.h:177
struct pcap_if pcap_if_t
Item in a list of interfaces, see pcap_if.
Definition incs/pcap.h:72
#define PCAP_ERRBUF_SIZE
Size to use when allocating the buffer that contains the libpcap errors.
Definition incs/pcap.h:59
void pcap_freealldevs(pcap_if_t *alldevsp)
Free an interface list returned by pcap_findalldevs().
int pcap_findalldevs_ex(char *source, struct pcap_rmtauth *auth, pcap_if_t **alldevs, char *errbuf)
Create a list of network devices that can be opened with pcap_open().
char * name
a pointer to a string giving a name for the device to pass to pcap_open_live()
Definition incs/pcap.h:150
struct pcap_if * next
if not NULL, a pointer to the next element in the list; NULL for the last element of the list
Definition incs/pcap.h:149
char * description
if not NULL, a pointer to a string giving a human-readable description of the device
Definition incs/pcap.h:151

Some comments about this code.

First of all, pcap_findalldevs_ex(), like other libpcap functions, has an errbuf parameter. This parameter points to a string filled by libpcap with a description of the error if something goes wrong.

Second, remember that not all the OSes supported by libpcap provide a description of the network interfaces, therefore if we want to write a portable application, we must consider the case in which description is null: we print the string "No description available" in that situation.

Note finally that we free the list with pcap_freealldevs() once when we have finished with it.

Let's try to compile and run the code of this first sample. In order to compile it under Unix or Cygwin, simply type:

  gcc -o testprog testprog.c -lpcap

On Windows, you will need to create a project, following the instructions in the Using WinPcap in your programs section of this manual. However, we suggest that you use the WinPcap developer's pack (available at the WinPcap website, http://www.winpcap.org ), since it provides many examples already configured as projects including all the code presented in this tutorial and the includes and libraries needed to compile and run the examples.

Assuming we have compiled the program, let's try to run it. On a particular WinXP workstation, the result we optained is

   1. \Device\NPF_{4E273621-5161-46C8-895A-48D0E52A0B83} (Realtek RTL8029(AS) Ethernet Adapter)
   2. \Device\NPF_{5D24AE04-C486-4A96-83FB-8B5EC6C7F430} (3Com EtherLink PCI) 

As you can see, the name of the network adapters (that will be passed to libpcap when opening the devices) under Windows are quite unreadable, so the parenthetical descriptions can be very helpful.

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