zeromq

The 0mq examples are, reasonably, all shown as sequences of calls directly in main(),
but for generic use I wanted to split up the work into small functions in a separate
'c' code file that could be called from main().

So i started by splitting up the calls into these three functions:

initZmqMsg( &zmqInfo );
a. lpzmqInfo->vpContext = zmq_init (1);
b. lpzmqInfo->vpSocket = zmq_socket (lpzmqInfo->vpContext, ZMQ_REQ);

sendZmqMsg( &zmqInfo, &zmqTrans );
c. zmq_msg_init_size (&lpzmqInfo->mtMsg, 5);
d. memcpy (zmq_msg_data (&lpzmqInfo->mtMsg), "Hello", 5);
e. zmq_connect (lpzmqInfo->vpSocket, "tcp://localhost:5555");
f. zmq_sendmsg (lpzmqInfo->vpSocket, &lpzmqInfo->mtMsg, 0);
g. zmq_msg_close (&lpzmqInfo->mtMsg);

termZmqMsg( &zmqInfo );
h. zmq_close (lpzmqInfo->vpSocket);
i. zmq_term (lpzmqInfo->vpContext)

To make this work I defined a structure to pass into the functions
as a parameter:

typedef struct ppmdbzmq_info {
void * vpContext;
void * vpSocket;
zmq_msg_t mtMsg;
char * cpMessage;
} PPMDB_ZMQ_INFO, *LPPPMDB_ZMQ_INFO;

Here's the problem :

A. when the vpSocket variable is passed in as a function parameter
struct member defined and declared externally:

- initZmqMsg(0 sets the lpzmqInfo->vpContext and lpzmqInfo->vpSocket Ok.
- cast to char ptrs and printf'd the results are definitely NOT null.
- szq_connect() returns 0 (success)
- szq_sendmsg() returns 5 (bytes sent)
- and hwserver does NOT receive the message!

B. I tried declaring the socket variable still as a member of a struct
but with the struct in the sendZmqMsg() function itself:

PPMDB_ZMQ_INFO zi;
LPPPMDB_ZMQ_INFO pzi = &zi;

setting the local struct context from the passed in context:
sendZmqMsg() On entry lpzmqInfo->vpContext=[a»_¦°S<]
pzi->vpContext = lpzmqInfo->vpContext;

then setting the local zi.vpSocket from the local zi.vpContext:
pzi->vpSocket = zmq_socket (&pzi->vpContext, ZMQ_REQ);

Well that doesn't work any better:
- zmq_socket() returns NULL
- zmq_connect() returns -1 (error)
- zmq_sendmsg() returns -1 (error)
- and hwserver does NOT receive the message!

C. Finally I just defined a local vpSocket variable in the function:

void * vpSocket;

vpSocket = zmq_socket (lpzmqInfo->vpContext, ZMQ_REQ);
nRet = zmq_connect (vpSocket, "tcp://localhost:5555");
nRet = zmq_sendmsg (vpSocket, &lpzmqInfo->mtMsg, 0);

Referencing a local vpSocket variable works. Which it should.

Why the message should get sent when the socket is a simple local variable and not when it's a member of a struct baffles me.

Hopefully someone will be able to point out the egregious error
i'm making.

The 0MQ version i'm using is 3.0.1 on Windows XP/Windows Server 2003
The application is a single threaded (/ML) client.
There are many transient clients and only one permanently online server.
Clients wake up, send a single message to the server, and terminate.

Thanks to anyone who can provide insight on this.