Jayson Ong Jayson Ong - 4 months ago 24
iOS Question

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

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.

Answer

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