cast from sockaddr * to sockaddr_in * increases required alignment

Question

The compiler produces this warning when I\'m working with some code which looks like -

....

for(p = res; p != NULL; p = p->ai_next) {
    void *addr;
           


        

Answer 1

To elaborate on the memcpy version. I thnk this is needed for ARM which cannot have misalligned data.

I created a struct that contains just the first two fields (I only needed port)

struct sockaddr_in_header {
    sa_family_t    sin_family; /* address family: AF_INET */
    in_port_t      sin_port;   /* port in network byte order */
};

Then to get the port out, I used memcpy to move the data to the stack

struct sockaddr_in_header   sinh;
unsigned short              sin_port;

memcpy(&sinh, conn->local_sockaddr, sizeof(struct sockaddr_in_header));

And return the port

sin_port = ntohs(sinh.sin_port);

This answer is really related to getting the port on Arm

How do I cast sockaddr pointer to sockaddr_in on Arm

The powers that be think that to be the same question as this one, however I dont want to ignore warnings. Experience has taught me that is a bad idea.