linux 下获取本机地址和掩码

Question

源码为：

#include <iostream>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <ifaddrs.h>

using namespace std;

int main(void) {
    struct ifaddrs* myaddrs;
    struct sockaddr_in *ss, *kk;
    if (getifaddrs(&myaddrs) == 0) {
        for (struct ifaddrs* ifa = myaddrs; ifa != NULL; ifa = ifa->ifa_next) {
        ss = (struct sockaddr_in*) ifa->ifa_addr;
        kk = (struct sockaddr_in*) ifa->ifa_netmask;
        if (ss->sin_family == AF_INET)
            cout << "sa_family:" << ss->sin_family << " " << ifa->ifa_name << ":" << inet_ntoa(ss->sin_addr) << " netmask:" << inet_ntoa(kk->sin_addr) << endl;
        }
    }
    return 0;
}

为什么得到的ip地址和子网掩码一样？

Answer 1

我感觉linux下的inet_ntoa打印子网掩码有问题，这段程序在Mac系统上可以正确输出。
我自己写了个函数，可以输出正确结果。

#include <iostream>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <ifaddrs.h>
#include <sstream>

using namespace std;

string getip(const sockaddr_in* addr)
{
    ostringstream s;
    int a = ntohl(addr->sin_addr.s_addr);
    s << ((a >> 24) & 0xFF) << '.' << ((a >> 16) & 0xFF) << '.'
      << ((a >> 8) & 0xFF) << '.' << (a & 0xFF);
    return s.str();
}


int main(void) 
{
    struct ifaddrs* myaddrs;
    struct sockaddr_in *ss, *kk;
    char buf[100];
    if (getifaddrs(&myaddrs) == 0) {
        for (struct ifaddrs* ifa = myaddrs; ifa != NULL; ifa = ifa->ifa_next) {
            ss = (struct sockaddr_in*) ifa->ifa_addr;
            kk = (struct sockaddr_in*) ifa->ifa_netmask;
            if (ss->sin_family == AF_INET)
                cout << ifa->ifa_name << ":" << getip(ss) << " netmask:" << getip(kk) << endl;
        }
    }
    return 0;
}

Answer 2

利用inet_ntop函数可以得到正确的结果