C program : how to list interfaces with a valid IP ?

Applications Programming
1

Hi all,

I think that the title is explicit enough :slight_smile: I would like in a C program to list the interfaces with a valid IP. Those that can permit to send something over a network.

Thanks :wink:

2

Having an IP address does not mean the routing is good enough to be able to send or receive anything over the interface.

I have been able to do so with getifaddrs() on Linux. Not sure other Unix flavours. Go search for manpage for that function.

3

Hi

You can use the "system" function from C, and you can call ifconfig like commands (i'm not sure that such command exist on UN*X, but it is possible). In that way you can list the interfaces. If you pipe the command with grep, you can also filter out which interfaces has a valid IP address.

Hope it helps

4

Stevens has a good example that is pretty compliant and portable.
Buy, beg or borrow Unix Network Programming if you don't already have a copy.

5

perhaps you need to write the survices by yourself,the interfaces should be designed thorouly .well,that's all what I know.

6

Who is 'Stevens' ? I'll look for this book thanks for the tip

7

Nice function ! That works but I have a problem with the assignment "ifcur = iflist" : error: incompatible types in assignment ?! I don't understand why.

	
...
struct ifaddrs*		iflist 
,		        ifcur ;
	
if (getifaddrs (&iflist) < 0)
	printf ("* Erreur getifaddrs ! \n") ;

ifcur = iflist ;
	
freeifaddrs(iflist);
...
8

Your declaration of struct ifaddrs* might be throwing off the compiler when it comes to a struct ifaddrs object and a pointer to that type. The argument to getifaddrs is a pointer to pointer to struct ifaddrs so use &ifcur instead of &iflist and since freeifaddrs takes a unilevel pointer use ifcur.

...
struct ifaddrs iflist, *ifcur
ifcur = &iflist;

if (getifaddrs (&ifcur) < 0)
	printf ("* Erreur getifaddrs ! \n") ;
	
freeifaddrs(ifcur);
...