Message queue won't read message of enum type

Question

I'm trying to use message queue to send and receive messages between father and son processes, I used enum to set message types for msgrcv but it seems that it ignores that information:

enum children {
  e_father_child1 = 1,
  e_father_child2 = 2,
  e_child1_father = 10,
  e_child2_father = 20
}; 

and the command is:

queue_indc = msgrcv (msgid, &msg, sizeof (msg.m_data), e_child1_father, 0);

It works if I change the argument from enum type to int but I was wondering why isn't it working as enum and is there any other way to make it work.

Thanks in advance!

Answer 1

It seems that msgtyp is treated as a long as opposed to just a regular int. And enums are treated as just regular ints.

ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg);

So I am thinking the compiler is having troubles converting an 'enum' to a long, where converting an 'int' to a long can be done more easily. What if you tried casting the msgtyp to a long? When I compiled the above code that you provided it worked without any cast however.

e.g.

queue_indc = msgrcv (msgid, &msg, sizeof (msg.m_data), (long) e_child1_father, 0);

Here is an article that may help explain the enum type:

http://www.embedded.com/electronics-blogs/programming-pointers/4026892/Enumerations-are-integers-except-when-they-re-not