Matt Brown – Journeys of a software engineer

April 5, 2009

How to get the IP address of an iPhone OS v2.2.1

Filed under: iPhone, Objective-C — Tags: , — mattbsoftware @ 11:35 pm

Lately I have been struggling with an iPhone OS 2.2.1 app that needs to know the WiFi IP address of the iPhone. Unfortunately at the time the app runs it does not have internet access and thus I cannot use whatismyip.com.

With thanks to Erica Sadun (iPhone cookbook) and gandreas and valexa on the iPhone dev forums I was able to create the following function. The function iterates over the IPs of the phone using getifaddrs(&addrs). if getWiFiIPAddress finds "en0" in the list interface addresses (ifaddrs) it will return the ethernet adapter zero (en0) IP address as a NSSring*. If no address is found the function will return NULL.

//------- includes

#include <ifaddrs.h>
#include
<arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/if_dl.h>
#include <arpa/inet.h>
#include <ifaddrs.h>

#if ! defined(IFT_ETHER)
#define IFT_ETHER 0x6/* Ethernet CSMACD */
#endif

//------- Implementation

- (NSString*)getWiFiIPAddress
{

BOOL success;
struct ifaddrs * addrs;
const struct ifaddrs * cursor;

success = getifaddrs(&addrs) == 0;
if (success) {
cursor = addrs;
while (cursor != NULL) {
if (cursor->ifa_addr->sa_family == AF_INET && (cursor->ifa_flags & IFF_LOOPBACK) == 0) // this second test keeps from picking up the loopback address
{
NSString *name = [NSString stringWithUTF8String:cursor->ifa_name];
if ([name isEqualToString:@"en0"]) { // found the WiFi adapter
return [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)cursor->ifa_addr)->sin_addr)];
}
}

cursor = cursor->ifa_next;
}
freeifaddrs(addrs);
}
return NULL;
}

PS: I need a better blog, that support snippets – comments?

Advertisements

Create a free website or blog at WordPress.com.