How to get the other devices' host name in the same wifi?

Question

I found some iOS app which could scan the local network and list all the device information.

I wonder how.

Pic:

Answer 1

Step 1 - Gel local IP

For iOS 7 and lower

#include <ifaddrs.h>
#include <arpa/inet.h>

- (NSString *)getIPAddress {

    NSString *address = @"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) {
        // Loop through linked list of interfaces
        temp_addr = interfaces;
        while(temp_addr != NULL) {
            if(temp_addr->ifa_addr->sa_family == AF_INET) {
                // Check if interface is en0 which is the wifi connection on the iPhone
                if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"]) {
                    // Get NSString from C String
                    address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];

                }

            }

            temp_addr = temp_addr->ifa_next;
        }
    }
    // Free memory
    freeifaddrs(interfaces);
    return address;

} 

iOS 8

[[NSHost currentHost] address]

Step 2 - Get online IPs

https://github.com/tonymillion/Reachability
Using Reachability, you can get subnet IP's reachability.

Reachability* reach = [Reachability reachabilityWithHostname:subnetIp];

Step 3 - Resolve hostname

Apple has a great article, which covers HostnameResolving topics. https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/NetworkingTopics/Articles/ResolvingDNSHostnames.html

You can try also simpler variant in iOS8

[[NSHost hostWithAddress:@"173.194.34.24"] name]

Example project

https://github.com/mongizaidi/LAN-Scan
here is a small project, that does the Local Area Network scan, you need only to resolve the hostnames, and you will get result that you want.