Question

Previous code :

struct Inet_address{
char v4[4];
};
extern "C" Inet_address Inet_loopback = 
{
  {127,0,0,1}
};

After modifying:

I have made Inet_address a union
Here Inet address is a union

union Inet_address{
char v4[4];
char v6[16];
};

Now I want to do the same operation on extern “C” Inet_address Inet_loopback
Say,

extern "C" Inet_address Inet_loopback = 
{
 if(some condition)
  {127,0,0,1}  //It should be Inet_address.v4
 else
    { 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1 }  //This should be Inet_address.v6
};

Please suggest a correct way to acheive this as I am getting error here.

Answer 1

You shouldn’t use char arrays for this – make a union out of in_addr and in6_addr:

typedef union {
    struct in_addr inaddr;
    struct in6_addr in6addr;
} in46_addr_t;

To set an ipv4 loopback address:

addr.inaddr.s_addr = INADDR_LOOPBACK;

For IPv6:

addr.in6addr = in6addr_loopback; // pre-defined global variable (note: assumes linux socket API)