从IP地址和子网掩码计算广播地址

Question

我想计算广播地址：

IP:     192.168.3.1
Subnet: 255.255.255.0
=       192.168.3.255

在C中。

我知道方法（在反转的IP和子网之间进行花式按位OR运算），但我的问题是我来自MacOSX Cocoa程序开发的绿色领域。

我查看了ipcal的源代码，但无法将其集成到我的代码库中。 必须有一个简单的十行代码在互联网上，我只是找不到它。 有人能指向一个简短的C语言代码示例吗？

- Kolja

Answer 1

只需要进行计算：

broadcast = ip | ( ~ subnet )

广播地址 = IP地址或反转的子网掩码。

在子网掩码为0的位置，广播地址对应的二进制位为1。

- froh42

Answer 2

我理解原帖作者至少对于位运算有一定的了解，但是在将字符串转换为数字以及反向操作上感到困惑。这里提供一个可用的（虽然测试较少）示例，使用froh42的计算方法。

jcomeau@aspire:~/rentacoder/jcomeau/freifunk$ cat inet.c; make inet; ./inet 192.168.3.1 255.255.255.0
#include <arpa/inet.h>
#include <stdio.h>
int main(int argc, char **argv) {
    char *host_ip = argc > 1 ? argv[1] : "127.0.0.1";
    char *netmask = argc > 2 ? argv[2] : "255.255.255.255";
    struct in_addr host, mask, broadcast;
    char broadcast_address[INET_ADDRSTRLEN];
    if (inet_pton(AF_INET, host_ip, &host) == 1 &&
        inet_pton(AF_INET, netmask, &mask) == 1)
        broadcast.s_addr = host.s_addr | ~mask.s_addr;
    else {
        fprintf(stderr, "Failed converting strings to numbers\n");
        return 1;
    }
    if (inet_ntop(AF_INET, &broadcast, broadcast_address, INET_ADDRSTRLEN) != NULL)
        printf("Broadcast address of %s with netmask %s is %s\n",
            host_ip, netmask, broadcast_address);
    else {
        fprintf(stderr, "Failed converting number to string\n");
        return 1;
    }
    return 0;
}
cc     inet.c   -o inet
Broadcast address of 192.168.3.1 with netmask 255.255.255.0 is 192.168.3.255

- jcomeau_ictx

Answer 3

可能吗？

unsigned broadcast(unsigned ip,unsigned subnet){
    unsigned int bits = subnet ^ 0xffffffff; 
    unsigned int bcast = ip | bits;

    return bcast;
}

编辑：我考虑到IP地址和子网掩码都没有“.”

- Tom

Answer 4

以下是C#中的实现方法。例如，使用IP地址10.28.40.149和子网掩码255.255.252.0返回正确的广播地址10.28.43.255，感谢这里提供的代码。

private static string GetBroadcastAddress(string ipAddress, string subnetMask) {
        //determines a broadcast address from an ip and subnet
        var ip = IPAddress.Parse(ipAddress);
        var mask = IPAddress.Parse(subnetMask);

        byte[] ipAdressBytes = ip.GetAddressBytes();
        byte[] subnetMaskBytes = mask.GetAddressBytes();

        if (ipAdressBytes.Length != subnetMaskBytes.Length)
            throw new ArgumentException("Lengths of IP address and subnet mask do not match.");

        byte[] broadcastAddress = new byte[ipAdressBytes.Length];
        for (int i = 0; i < broadcastAddress.Length; i++) {
            broadcastAddress[i] = (byte)(ipAdressBytes[i] | (subnetMaskBytes[i] ^ 255));
        }
        return new IPAddress(broadcastAddress).ToString();
    }

- Jason Jakob

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问题标记为“C”，而不是“C#”。 - gre_gor

Answer 5

好的，未来需要查找此代码的人。我今天花了一些时间，因为我需要它，这里是完整的代码，它可以正常工作 :) 只需复制并粘贴它，然后导入所需的dll文件。

private IPAddress CalculateBroadCastAddress(IPAddress currentIP, IPAddress ipNetMask)
    {
        string[] strCurrentIP = currentIP.ToString().Split('.');
        string[] strIPNetMask = ipNetMask.ToString().Split('.');

        ArrayList arBroadCast = new ArrayList();

        for (int i = 0; i < 4; i++)
        {
            int nrBCOct = int.Parse(strCurrentIP[i]) | (int.Parse(strIPNetMask[i]) ^ 255);
            arBroadCast.Add(nrBCOct.ToString());
        }
        return IPAddress.Parse(arBroadCast[0] + "." + arBroadCast[1] +
               "." + arBroadCast[2] + "." + arBroadCast[3]);
    }


    private IPAddress getIP()
    {
        IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
        foreach (IPAddress ip in host.AddressList)
        {
            if (ip.AddressFamily == AddressFamily.InterNetwork)
            {
                return ip;

            }
        }
        return null;
    }

    private IPAddress getSubnetMask()
    {
        NetworkInterface[] Interfaces = NetworkInterface.GetAllNetworkInterfaces();
        IPAddress ip = getIP();
        foreach (NetworkInterface interf in Interfaces)
        {

            UnicastIPAddressInformationCollection UnicastIPInfoCol = interf.GetIPProperties().UnicastAddresses;

            foreach (UnicastIPAddressInformation UnicatIPInfo in UnicastIPInfoCol)
            {
                if (UnicatIPInfo.Address.Equals(ip))
                    return UnicatIPInfo.IPv4Mask;
            }

        }

        return null;

    }

然后就像这样调用它：

IPAddress  broadcastip = CalculateBroadCastAddress(getIP(), getSubnetMask());

开心编程 :)

- Zardaloop

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这不是C语言。 - Markaos