read/write struct to a socket

Question

I am trying to write from client a struct to the server with socket.

the struct is :

typedef struct R
{
int a;
int b;
double c;
double d;
double result[4]; 
}R;

The struct is the same at the 2 programs(server,client) and i malloc for the struct in both.

the client program:

struct R* r;

malloc..

...(fill the struct with data)

write(socket_fd,(void*)r,size of(R));

the Server program:

struct R* r;

malloc..

read(client_fd,(R*)r,size of(R));

This is not passing the struct from client to server..

How to write the struct to the server by socket??

What you show looks ok, however there are a lots of other things (that you do not show) that could be/go wrong when transmitting data via sockets. — alk
like what? i tryied to sent just int or double and it is working... but the struct not — user2501289
Assuming memory handling and socket setup and connect/accept is done properly, endianness and padding aren't an issue, then closely read the documentation for read()/write() and learn that those two functions (at least for sockets) do not necessarily read/wrtite as much bytes as they were told to, but few. So looping around such calls counting until all data expected had been read/written is a good idea, not to say an essential necessity. — alk

fkl fkl · Accepted Answer · 2014-04-29T16:46:19

Some basic elements of network programming are:

One read or write call might not write the total bytes you intend to read/write. Check the return value of call. It would return number of bytes read/written. If less bytes have been written, you should call write in a loop until all data has been written. Same applies to read.
Endianess of machine also matters. If you wrote an int which was little endian (e.g. x86), when travelling on the network it would be converted into a big endian value. You need to use apis such as htons, ntohs in POSIX to accommodate that.

These are just starting points, but the most likely reasons of data not reaching destination in the form as you expected.