Function does not see field of struct inside struct - c

Question

So, I have to do library sending IPv4 packets (without libraries with prepared headers) and problem is that I can't access field in struct inside struct while using function, though eclipse does not see error, hint does not show that is possible.
Structs:
struct packet{
struct ipv4hdr * iphdr;
struct icmphdr * icmphdr;
char * data;
};
struct ipv4hdr{
u_int8_t version_length;
u_int8_t type;
u_int16_t total_length;
u_int16_t id;
u_int16_t frag_off;
u_int8_t ttl;
u_int8_t protocol;
u_int16_t checksum;
u_int32_t source;
u_int32_t destination;
};
Pointers to function (that is requirement, both work):
struct packet *(*packetCreate)() = dlsym(lib, "createPacket");
void (*setIP)(struct packet *, u_int8_t, u_int8_t, u_int16_t, char*, u_int8_t, char*) = dlsym(lib, "prepareIP");
Creation of struct packet:
struct packet * createPacket(){
struct packet * pack= malloc(sizeof(struct packet));
return pack;
}
Now, calling fields inside main does show posssible fields:
struct packet * pack = packetCreate();
pack->iphdr->(CTRL+space displays all the fields) //and eclipse automatically corrects all the . to ->
Meanwhile calling created pointer on function does not display fields while using hint and that causes segmentation fault (core dumped):
void prepareIP(struct packet * packet, u_int8_t length, u_int8_t type, u_int16_t id, char* destination, u_int8_t ttl, char *data){
packet->iphdr->type = type; //it is not treated by error, though any field causes crash
//meanwhile hint
packet->iphdr->(CTRL+space gets)ipv4hdr;
}
Question again is why I can't call specific field inside function that points to the original struct and how to do this inside that function

Answer 1

It looks like you forgot to allocate space for struct ipv4hdr * iphdr;.
But maybe this isn't even what you intended. Do you really want iphdr to be a pointer in your struct? It makes mucht more sense, if it was part of the struct, like this:
struct packet{
struct ipv4hdr iphdr; // notice that we do not use pointers here!
struct icmphdr icmphdr; // this looks curious to me - we have either an IP or an ICMP package, why both headers in the same package?
char * data;
};