Send and receive uint32_t over a socket via iovec-CodePudding

I'm trying to send a uint_32t type variable over iovec sturct over unix domain socket.

My iovec declaration:

uint32_t request_id = 123456;
struct iovec io = { .iov_base = &request_id, .iov_len = sizeof(uint32_t) };

on the receiving side:

char dup[4];
struct iovec io = { .iov_base = dup, .iov_len = sizeof(dup) };
msg.msg_iov = &io;

When I print msg.msg_iov[0].iov_base I get a different number every time.

printf("msg.msg_iov[0].iov_base = %d\n", msg.msg_iov[0].iov_base); => 723905316

I guess something is off with bytes-to-uint32 conversion?

CodePudding user response：

When I print msg.msg_iov[0].iov_base I get a different number every time.

Yes, on the sending side it's the address of request_id and on the receiving side it's address of dup. These addresses do however not matter. They are only used to tell writev and readv where to read/write the data and they will often be different each time you start the programs.

Example:

Sender:

uint32_t request_id = htonl(123456); // to network byte order from host byte order
iovec io = { .iov_base = &request_id, .iov_len = sizeof(uint32_t) };
writev(fd, &io, 1);

Receiver:

uint32_t request_id;
iovec io = { .iov_base = &request_id, .iov_len = sizeof(uint32_t) };
readv(fd, &io, 1);
request_id = ntohl(request_id); // from network byte order to host byte order

CodePudding user response：

Your code is printing the address, not the integer.

Assuming no endianess issues, then something like this should work

printf("msg.msg_iov[0].iov_base = %d\n", *(int32_t*)msg.msg_iov[0].iov_base);

This code does assume that %d can successfully print a int32_t something I don't think is guaranteed to be true. If that's a problem you could try this

int temp = *(int32_t*)msg.msg_iov[0].iov_base;
printf("msg.msg_iov[0].iov_base = %d\n", temp);