Apportable gives compile error "arithmetic on a pointer to an incomplete type"

Question

Apportable error

arithmetic on a pointer to an incomplete type 'struct if_msghdr'
socketStruct = (struct sockaddr_dl *) (interfaceMsgStruct + 1);

Here is the code. The code is working fine on ios/xcode but gives above error to interfaceMsgStruct with apportable. I have get this code from google and it is widely used so i dont think the code might have error. If it does then please correct me.

#import "MFMacAddress.h"

@implementation MFMacAddress

#include <sys/socket.h>
#include <sys/sysctl.h>
#include <net/if.h>
#include <net/if_dl.h>



+ (NSString *)getMacAddress
{
    int                 mgmtInfoBase[6];
    char                *msgBuffer = NULL;
    size_t              length;
    unsigned char       macAddress[6];
    struct if_msghdr    *interfaceMsgStruct;
    struct sockaddr_dl  *socketStruct;
    NSString            *errorFlag = NULL;

    // Setup the management Information Base (mib)
    mgmtInfoBase[0] = CTL_NET;        // Request network subsystem
    mgmtInfoBase[1] = AF_ROUTE;       // Routing table info
    mgmtInfoBase[2] = 0;
    mgmtInfoBase[3] = AF_LINK;        // Request link layer information
    mgmtInfoBase[4] = NET_RT_IFLIST;  // Request all configured interfaces

    // With all configured interfaces requested, get handle index
    if ((mgmtInfoBase[5] = if_nametoindex("en0")) == 0)
        errorFlag = @"if_nametoindex failure";
    else
    {
        // Get the size of the data available (store in len)
        if (sysctl(mgmtInfoBase, 6, NULL, &length, NULL, 0) < 0)
            errorFlag = @"sysctl mgmtInfoBase failure";
        else
        {
            // Alloc memory based on above call
            if ((msgBuffer = malloc(length)) == NULL)
                errorFlag = @"buffer allocation failure";
            else
            {
                // Get system information, store in buffer
                if (sysctl(mgmtInfoBase, 6, msgBuffer, &length, NULL, 0) < 0)
                    errorFlag = @"sysctl msgBuffer failure";
            }
        }
    }

    // Befor going any further...
    if (errorFlag != NULL)
    {
        NSLog(@"Error: %@", errorFlag);
        return errorFlag;
    }

    // Map msgbuffer to interface message structure
    interfaceMsgStruct = (struct if_msghdr *) msgBuffer;

    // Map to link-level socket structure
    socketStruct = (struct sockaddr_dl *) (interfaceMsgStruct + 1);

    // Copy link layer address data in socket structure to an array
    memcpy(&macAddress, socketStruct->sdl_data + socketStruct->sdl_nlen, 6);

    // Read from char array into a string object, into traditional Mac address format
    NSString *macAddressString = [NSString stringWithFormat:@"%02X:%02X:%02X:%02X:%02X:%02X",
                                  macAddress[0], macAddress[1], macAddress[2],
                                  macAddress[3], macAddress[4], macAddress[5]];
    NSLog(@"Mac Address: %@", macAddressString);

    // Release the buffer memory
    free(msgBuffer);

    return macAddressString;
}

@end

Answer 1

To get the mac address, you can do

[[UIDevice currentDevice] macAddress]

which returns an NSString *

The compile error you're seeing is the result of a different system headers between IOS and Android. We're working on a more transparent solution, but in the meantime the solution above is an easy workaround.

Answer 2

Often you get this error when the definition of struct if_msghdr is not 'visible'.

Check if you need to #include other header files, or if different conditional compilation options locked it out.