Calculating the Broadcast Address in Objective-C

Question

How do I go about calculating the Broadcast Address in Objective C

I would like to have the Broadcast Address resolve to the same result as shown in the following Subnet Calculator - http://www.subnet-calculator.com/subnet.php

I have the IP Address of my local IOS device and the Subnet Mask. And I know that the Broadcast Address uses the following formula

broadcast = ip | ( ~ subnet )

(I am answering my self, as I have not seen this on the Internet anywhere, and also I am not aware of any libraries which perform this calculation. Happy to see if anyone else has a better solution or is aware of any libraries)

Answer 1

Alternative solution:

#include <net/ethernet.h>
#include <arpa/inet.h>

NSString *localIPAddress = @"192.168.1.10";
NSString *netmaskAddress = @"255.255.192.0";

// Strings to in_addr:
struct in_addr localAddr;
struct in_addr netmaskAddr;
inet_aton([localIPAddress UTF8String], &localAddr);
inet_aton([netmaskAddress UTF8String], &netmaskAddr);

// The broadcast address calculation:
localAddr.s_addr |= ~(netmaskAddr.s_addr);

// in_addr to string:
NSString *broadCastAddress = [NSString stringWithUTF8String:inet_ntoa(localAddr)];

Answer 2

You don't need to provide IP address & subnet-mask to calculate "Broadcast" address of any network interface. Actually you don't need to manually calculate it.

There is ifaddrs Structure that describes a network host. It provides complete details of any network interface. By using getifaddrs() method, you can retrieve Broadcast address of the network without providing IP & subnet mask as attribute. Function itself retrieves the details. I'd prefer this because this will make code more generic.

I am using this in my code.

#import <ifaddrs.h> // for interface addresses needed to find local IP

static NSString * broadcastAddress()
//Gets Local IP of the device over Wifi
//Calculates & returns broadcast Address for the network
{
    NSString * broadcastAddr= @"Error";
    struct ifaddrs *interfaces = NULL;
    struct ifaddrs *temp_addr = NULL;
    int success = 0;

    // retrieve the current interfaces - returns 0 on success
    success = getifaddrs(&interfaces);

    if (success == 0)
    {
        temp_addr = interfaces;

        while(temp_addr != NULL)
        {
            // check if interface is en0 which is the wifi connection on the iPhone
            if(temp_addr->ifa_addr->sa_family == AF_INET)
            {
                if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])
                {
                    broadcastAddr = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_dstaddr)->sin_addr)];

                }
            }

            temp_addr = temp_addr->ifa_next;
        }
    }

    freeifaddrs(interfaces);
    return broadcastAddr;
}

To know more about ifaddrs structure See this