CocoaDev

taken from: http://developer.apple.com/mac/library/samplecode/GetPrimaryMACAddress/Introduction/Intro.html

compile with:

gcc -Wall -O3 -x objective-c -fobjc-exceptions -framework Foundation -framework CoreFoundation \
    -framework IOKit -o GetPrimaryMACAddress GetPrimaryMACAddress.c

File:           GetPrimaryMACAddress.c

Description:    This sample application demonstrates how to do retrieve the Ethernet MAC
                address of the built-in Ethernet interface from the I/O Registry on Mac OS X.
                Techniques shown include finding the primary (built-in) Ethernet interface,
                finding the parent Ethernet controller, and retrieving properties from the
                controller's I/O Registry entry.
            
Copyright:      Copyright 2001-2005 Apple Computer, Inc. All rights reserved.

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Change History (most recent first):
    
        <3>     09/15/05    Updated to produce a universal binary. Use kIOMasterPortDefault
                            instead of older IOMasterPort function. Print the MAC address
                            to stdout in response to <rdar://problem/4021220>.
        <2>     04/30/02    Fix bug in creating the matching dictionary that caused the
                            kIOPrimaryInterface property to be ignored. Clean up comments and add
                            additional comments about how IOServiceGetMatchingServices operates.
        <1>     06/07/01    New sample.

// Ethernet interfaces are instances of class kIOEthernetInterfaceClass. 
// IOServiceMatching is a convenience function to create a dictionary with the key kIOProviderClassKey and 
// the specified value.
matchingDict = IOServiceMatching(kIOEthernetInterfaceClass);

// Note that another option here would be:
// matchingDict = IOBSDMatching("en0");
    
if (NULL == matchingDict) {
    printf("IOServiceMatching returned a NULL dictionary.\n");
}
else {
    // Each IONetworkInterface object has a Boolean property with the key kIOPrimaryInterface. Only the
    // primary (built-in) interface has this property set to TRUE.
    
    // IOServiceGetMatchingServices uses the default matching criteria defined by IOService. This considers
    // only the following properties plus any family-specific matching in this order of precedence 
    // (see IOService::passiveMatch):
    //
    // kIOProviderClassKey (IOServiceMatching)
    // kIONameMatchKey (IOServiceNameMatching)
    // kIOPropertyMatchKey
    // kIOPathMatchKey
    // kIOMatchedServiceCountKey
    // family-specific matching
    // kIOBSDNameKey (IOBSDNameMatching)
    // kIOLocationMatchKey
    
    // The IONetworkingFamily does not define any family-specific matching. This means that in            
    // order to have IOServiceGetMatchingServices consider the kIOPrimaryInterface property, we must
    // add that property to a separate dictionary and then add that to our matching dictionary
    // specifying kIOPropertyMatchKey.
        
    propertyMatchDict = CFDictionaryCreateMutable(kCFAllocatorDefault, 0,
                                                  &kCFTypeDictionaryKeyCallBacks,
                                                  &kCFTypeDictionaryValueCallBacks);

    if (NULL == propertyMatchDict) {
        printf("CFDictionaryCreateMutable returned a NULL dictionary.\n");
    }
    else {
        // Set the value in the dictionary of the property with the given key, or add the key 
        // to the dictionary if it doesn't exist. This call retains the value object passed in.
        CFDictionarySetValue(propertyMatchDict, CFSTR(kIOPrimaryInterface), kCFBooleanTrue); 
        
        // Now add the dictionary containing the matching value for kIOPrimaryInterface to our main
        // matching dictionary. This call will retain propertyMatchDict, so we can release our reference 
        // on propertyMatchDict after adding it to matchingDict.
        CFDictionarySetValue(matchingDict, CFSTR(kIOPropertyMatchKey), propertyMatchDict);
        CFRelease(propertyMatchDict);
    }
}

// IOServiceGetMatchingServices retains the returned iterator, so release the iterator when we're done with it.
// IOServiceGetMatchingServices also consumes a reference on the matching dictionary so we don't need to release
// the dictionary explicitly.
kernResult = IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, matchingServices);    
if (KERN_SUCCESS != kernResult) {
    printf("IOServiceGetMatchingServices returned 0x%08x\n", kernResult);
}
    
return kernResult; }

// Make sure the caller provided enough buffer space. Protect against buffer overflow problems.
if (bufferSize < kIOEthernetAddressSize) {
    return kernResult;
}

// Initialize the returned address
bzero(MACAddress, bufferSize);

// IOIteratorNext retains the returned object, so release it when we're done with it.
while ( (intfService = IOIteratorNext(intfIterator)) )
{
    CFTypeRef   MACAddressAsCFData;        

    // IONetworkControllers can't be found directly by the IOServiceGetMatchingServices call, 
    // since they are hardware nubs and do not participate in driver matching. In other words,
    // registerService() is never called on them. So we've found the IONetworkInterface and will 
    // get its parent controller by asking for it specifically.
    
    // IORegistryEntryGetParentEntry retains the returned object, so release it when we're done with it.
    kernResult = IORegistryEntryGetParentEntry(intfService,
                                               kIOServicePlane,
                                               &controllerService);
    
    if (KERN_SUCCESS != kernResult) {
        printf("IORegistryEntryGetParentEntry returned 0x%08x\n", kernResult);
    }
    else {
        // Retrieve the MAC address property from the I/O Registry in the form of a CFData
        MACAddressAsCFData = IORegistryEntryCreateCFProperty(controllerService,
                                                             CFSTR(kIOMACAddress),
                                                             kCFAllocatorDefault,
                                                             0);
        if (MACAddressAsCFData) {
            CFShow(MACAddressAsCFData); // for display purposes only; output goes to stderr
            
            // Get the raw bytes of the MAC address from the CFData
            CFDataGetBytes(MACAddressAsCFData, CFRangeMake(0, kIOEthernetAddressSize), MACAddress);
            CFRelease(MACAddressAsCFData);
        }
            
        // Done with the parent Ethernet controller object so we release it.
        (void) IOObjectRelease(controllerService);
    }
    
    // Done with the Ethernet interface object so we release it.
    (void) IOObjectRelease(intfService);
}
    
return kernResult; }

// NSLog( @"Found one of more valid interfaces. Extracting MAC addresses..." );

NSDictionary* intfDictionary = GetMACAddresses( intfIterator );

/*
for( id key in intfDictionary ) {
  NSLog( @"  %@  =>  %@", key, [intfDictionary objectForKey: key] );
}    */

IOObjectRelease( intfIterator );   }

kernResult = IORegistryEntryGetParentEntry( interfaceService,
                                            kIOServicePlane,
                                            &controllerService );
if( KERN_SUCCESS != kernResult ) {
  printf( "IORegistryEntryGetParentEntry failed with 0x%08x\n", kernResult );
} else {
  MACAddrAsCFData = IORegistryEntryCreateCFProperty( controllerService,
                                                     CFSTR(kIOMACAddress),
                                                     kCFAllocatorDefault,
                                                     0 );
  
  BSDNameAsCFString = IORegistryEntryCreateCFProperty( interfaceService,
                                                       CFSTR("BSD Name"),
                                                       kCFAllocatorDefault,
                                                       0 );
  
  if( MACAddrAsCFData && BSDNameAsCFString ) {
    if( nil == etherDictionary ) {
      etherDictionary = [[NSMutableDictionary alloc] init]; 
    }
    
    [etherDictionary setObject:bytesToHexString((NSData*)MACAddrAsCFData)
                        forKey:(NSString*)BSDNameAsCFString];
    
  }

  if( nil != BSDNameAsCFString ) {
        CFRelease( BSDNameAsCFString );
  }

  if( nil != MACAddrAsCFData ) {
        CFRelease( MACAddrAsCFData );
  }
}   }

  bsdName = (CFStringRef) IORegistryEntrySearchCFProperty (usb_device_ref,
                                                           kIOServicePlane,
                                                           CFSTR ( kIOBSDNameKey ),
                                                           kCFAllocatorDefault,
                                                           kIORegistryIterateRecursively );
  if (!bsdName) continue;

  deviceName = [[NSString stringWithFormat: @"%@", bsdName] UTF8String];

  //printf("%s\n", deviceName);

  devicePath[0] = '\0';
  strcat(devicePath, "/dev/");
  strcat(devicePath, deviceName);

  pathlen = strlen(devicePath);

  //printf("pathlen: %zu\n", pathlen);
  //printf("devicePath: %s\n", devicePath);

  for (i = 0; i < num_stat; i++) {

     if (strncmp(buf[i].f_mntfromname, devicePath, pathlen) == 0)
     {
        if ( print0 == 0 )
           fprintf(stdout, "%s %s\n", buf[i].f_mntfromname, buf[i].f_mntonname);
        else
           fprintf(stdout, "%s %s%c", buf[i].f_mntfromname, buf[i].f_mntonname, 0);  
           // null-terminate output (ASCII nul character)
     }

  }

  CFRelease(bsdName);

  IOObjectRelease(usb_device_ref);            // no longer need this reference