Undefined symbols for architecture arm64: "getdefaultgateway(unsigned int*)"

Question

I'm trying to get the gateway ip address of the wifi I'm connected to. I'm using the answer in this question but I'm getting an error on the codes.

When I use this in my project

- (NSString *)getGatewayIP {
    NSString *ipString = nil;
    struct in_addr gatewayaddr;
    int r = getdefaultgateway(&(gatewayaddr.s_addr));
    if(r >= 0) {
        ipString = [NSString stringWithFormat: @"%s",inet_ntoa(gatewayaddr)];
        NSLog(@"default gateway : %@", ipString );
    } else {
        NSLog(@"getdefaultgateway() failed");
    }

    return ipString;
}

I get this error when I try to build my project:

Undefined symbols for architecture arm64: "getdefaultgateway(unsigned int*)"

Here is the getgateway.c

int getdefaultgateway(in_addr_t * addr)
{
    int mib[] = {CTL_NET, PF_ROUTE, 0, AF_INET,
        NET_RT_FLAGS, RTF_GATEWAY};
    size_t l;
    char * buf, * p;
    struct rt_msghdr * rt;
    struct sockaddr * sa;
    struct sockaddr * sa_tab[RTAX_MAX];
    int i;
    int r = -1;
    if(sysctl(mib, sizeof(mib)/sizeof(int), 0, &l, 0, 0) < 0) {
        return -1;
    }
    if(l>0) {
        buf = malloc(l);
        if(sysctl(mib, sizeof(mib)/sizeof(int), buf, &l, 0, 0) < 0) {
            return -1;
        }
        for(p=buf; p<buf+l; p+=rt->rtm_msglen) {
            rt = (struct rt_msghdr *)p;
            sa = (struct sockaddr *)(rt + 1);
            for(i=0; i<RTAX_MAX; i++) {
                if(rt->rtm_addrs & (1 << i)) {
                    sa_tab[i] = sa;
                    sa = (struct sockaddr *)((char *)sa + ROUNDUP(sa->sa_len));
                } else {
                    sa_tab[i] = NULL;
                }
            }

            if( ((rt->rtm_addrs & (RTA_DST|RTA_GATEWAY)) == (RTA_DST|RTA_GATEWAY))
               && sa_tab[RTAX_DST]->sa_family == AF_INET
               && sa_tab[RTAX_GATEWAY]->sa_family == AF_INET) {


                if(((struct sockaddr_in *)sa_tab[RTAX_DST])->sin_addr.s_addr == 0) {
                    char ifName[128];
                    if_indextoname(rt->rtm_index,ifName);

                    if(strcmp("en0",ifName)==0){

                        *addr = ((struct sockaddr_in *)(sa_tab[RTAX_GATEWAY]))->sin_addr.s_addr;
                        r = 0;
                    }
                }
            }
        }
        free(buf);
    }
    return r;
}

Do I need to add frameworks? I've got no idea how to make it work.

You should probably check to see if the .c file is even being compiled by Xcode. if you put a line of garbage code into the `getdefaultgateway` function, does Xcode stop compiling and throw an error there? — Michael Dautermann, Jul 27 '16 at 08:58
Yup , I just checked it and .c gets compiled. Maybe it has to do something with my class having .mm extensions? I had problems before when my class doesn't accept automatic casting. — Jongers, Jul 27 '16 at 09:08

score 1 · Accepted Answer · edited May 23 '17 at 12:02

1

Yes. .mm was my next question to you.

You're running into C++ name mangling issues.

In whichever .h file where you define and ultimately include/import the getdefaultgateway function, add this before:

#ifdef __cplusplus
extern "C" {
#endif

and after:

#ifdef __cplusplus
}
#endif

edited May 23 '17 at 12:02

Community

1
1

answered Jul 27 '16 at 09:11

Michael Dautermann

88,797
17
166
215

That's great bro! Where did you learn that? I tried adding codes that I think of to make something work like casting, etc. but I probably couldn't think of doing that. High five! – Jongers Jul 27 '16 at 09:15

Undefined symbols for architecture arm64: "getdefaultgateway(unsigned int*)"

1 Answers1