91.515. OS-1 Fall 2010

The problems I pointed out in class with our message
queue example were caused by the declaration of MSG.mtype,
the message type component in the message structure I used:

Previous incorrect structure declaration:

typedef struct{
   int  mtype;
   char mtext[252];
} MSG;o

The man page states clearly that the type field must be of
type long (not int).  While an int and a long are both 4 bytes
on a 32 bit system, they are 4 and 8 bytes respectively
on a 64 bit system, so my failure to declare mtype to be a long
was the cause of our run-time problems.  The correct declaration
and treatment of the structure should have been:

Current correct structure declaration:

typedef struct{
   long mtype;
   char mtext[252];
} MSG;

This resolves the problem.  The sources for  client_msg.c  and
server_msg.c   in    ~bill/cs515/msg_ipc_example    and at
www.cs.uml.edu/~bill/cs515/msg_ipc_example    have been updated
to reflect the type change.