While it is true that compilers pad for alignment it is pretty easy to avoid that, at least in my experience. So an easier approach, but more fragile, is just

While it is true that compilers pad for alignment it is pretty easy to avoid that, at least in my experience. So an easier approach, but more fragile, is just to define the struct, count up how big you think it should be and then do an assert(sizeof(struct foo) == FOO_SIZE); If that assert doesn't pop then you can just do write(fd, &foo, FOO_SIZE); I know that is a lot less elegant but it works and isn't doing the translation back and forth. If you don't like that you might consider using Sun's RPC marshalling code that is (used to be?) part of Linux.