获取本地网关ip

获取本地网关ip的c源码：

int getWanGateway(char *gateway)
{
    char buff[256];
    int nl = 0;
    struct in_addr dest;
    struct in_addr gw;
    int flgs, ref, use, metric;
    unsigned long int d, g, m;
    int find_default_flag = 0;
    char sgw[16];

    FILE *fp = fopen("/proc/net/route", "r");

    while (fgets(buff, sizeof (buff), fp) != NULL)
    {
        if (nl)
        {
            int ifl = 0;
            while (buff[ifl] != ' ' && buff[ifl] != '\t' && buff[ifl] != '\0')
                ifl++;
            buff[ifl] = 0; /* interface */
            if (sscanf(buff + ifl + 1, "%lx%lx%X%d%d%d%lx",
                    &d, &g, &flgs, &ref, &use, &metric, &m) != 7)
            {
                fclose(fp);
                return -1;
            }

            if (flgs & RTF_UP)
            {
                dest.s_addr = d;
                gw.s_addr = g;
                strcpy(sgw, (gw.s_addr == 0 ? "" : (char *) inet_ntoa(gw)));

                if (dest.s_addr == 0)
                {
                    find_default_flag = 1;
                    memcpy(gateway, sgw, strlen(sgw));
                    printf("gateway:%s\n", gateway);
                    break;
                }
            }
        }
        nl++;
    }
    fclose(fp);

    if (find_default_flag == 1)
        return 0;
    else
        return -1;
}