Linux 获取网关地址

route命令的用法：操作或者显示IP路由表
route：DESCRIPTION
Route manipulates the kernel's IP routing tables. Its primary use is to set up static routes to
specific hosts or networks via an interface after it has been configured with the ifconfig(8) pro‐gram.

When the add or del options are used, route modifies the routing tables. Without these options,
route displays the current contents of the routing tables.
route-n:(用于打印路由表)
show numerical addresses instead of trying to determine symbolic host names. This is useful
if you are trying to determine why the route to your nameserver has vanished.

一、在Linux下查看路由表：

(1)用命令route -n

root@Ubunut10:~# route -n
内核 IP 路由表
目标            网关            子网掩码        标志  跃点   引用  使用 接口
               eth1
               eth1

(2)cat /pro/net/route

root@Ubunut10:/proc/net# cat route
Iface    Destination    Gateway     Flags    RefCnt    Use    Metric    Mask        MTU    Window    IRTT
eth1    　　007BA8C0            　　    　　    　　    　　00FFFFFF    　　
eth1    　　    FE7BA8C0        　　    　　    　　    　　    　　         

二、实现代码：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <ctype.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>

#include <arpa/inet.h>

int get_gateway_addr(char *gateway_addr)
{
    ];
     ;
    struct in_addr gw;
    int flgs, ref, use, metric;
    unsigned long int d,g,m;
    unsigned long addr;

    FILE *fp = NULL;

    fp = fopen("/proc/net/route", "r");
    if (fp == NULL)
    {
        ;
    }

    nl =  ;
    memset(buff, ,sizeof(buff));
    while( fgets(buff, sizeof(buff), fp) != NULL )
    {
        if(nl)
        {
            ;
            while(buff[ifl]!=' ' && buff[ifl]!='\t' && buff[ifl]!='\0')
                ifl++;
            buff[ifl]=;    /* interface */
            , "%lx%lx%X%d%d%d%lx",
                   &d, &g, &flgs, &)
            {
                fclose(fp);
                ;
            }

            ifl = ;        /* parse flags */
            //if(flgs&RTF_UP)
            //{
                gw.s_addr   = g;

                )
                {
                    strcpy(gateway_addr, inet_ntoa(gw));
                    fclose(fp);
                    ;
                }
            //}
        }
        nl++;
    }    

    if(fp)
    {
        fclose(fp);
        fp = NULL;
    }

    ;
}

int main()
{

    ] = {};
     get_gateway_addr(gateway_addr);
    printf("gateway_addr:%s\n", gateway_addr);
    ;
}

三、运行结果：

gateway_addr:192.168.123.254