A Program to Read a Message

The next program, receive.c, reads and prints out the contents of the message being published from the send.c program described in the previous section.

Step 7

Copy the program receive.c into your tutorial directory. Under Windows also copy the associated makefile, recvw32m.mak, into your tutorial directory. Here is an example of the receive.c program:

    /* receive.c - read and print an INFO message */ 
    /* $RTHOME/examples/smrtsock/tutorial/lesson1/receive.c */ 
 
1   #include <rtworks/ipc.h> 
 
2   int main(int argc, char **argv) 
    {   
3     T_IPC_MSG msg; 
4     T_STR msg_text; 
  
5     TipcSrvSubjectSetSubscribe("/tutorial/lesson1", TRUE); 
 
6     msg = TipcSrvMsgNext(T_TIMEOUT_FOREVER); 
7     TipcMsgSetCurrent(msg, 0); 
8     TipcMsgNextStr(msg, &msg_text); 
9     TutOut("Text from message = %s\n", msg_text); 
 
10    TipcSrvDestroy(T_IPC_SRV_CONN_NONE); 
 
      } /* main */

As with the send.c program, notice how the program consists of so few lines of code. Compare this with a similar program written using pipes, sockets or shared memory. Not only are TIBCO SmartSockets programs much shorter, they also have many built-in features (such as automatic data conversion across heterogeneous platforms). Let’s examine this program on a line-by-line basis to understand in detail how the program works:


Line 1	The include file `ipc.h` is required.
Line 3	Declares a TIBCO SmartSockets message (this is eventually used to hold the incoming message).
Line 4	Declares a string into which you eventually transfers the data part of the message.
Line 5	The call to TipcSrvSubjectSetSubscribe performs two tasks: Establishes a connection to RTserver (this might include auto-starting RTserver), because there was no explicit call to connect to RTserver. Informs RTserver to forward any message that has been published to the `/tutorial/lesson1` subject by any client in the project. The second parameter (`TRUE`) specifies that the program wishes to start subscribing to the subject.
Line 6	The call to TipcSrvMsgNext retrieves the next message in the program’s message queue from RTserver. The T_TIMEOUT_FOREVER constant specifies that the function blocks (waits) forever for a message. You can specify an actual time-out period for this argument; for example, 10.0 would mean the function returns a NULL value after 10 seconds if no message has become available.
Line 7	You now have a message to work with. The call to TipcMsgSetCurrent sets the message pointer (the current field) to the first field in the data part of the message.
Line 8	The call to TipcMsgNextStr gets the next string field from the data part of the message (in this case, it is the first and only field) and places it in `msg_text`. In this example it contains the string `"Hello World!".`
Line 9	This line calls the TIBCO SmartSockets utility function `TutOut` to output the contents of `msg_text`.
Line 10	The last line of the program gracefully disconnects from RTserver with a call to TipcSrvDestroy.

Step 8

Now you must compile and link the receiving program in a similar manner as before:

Step 9

Under Windows, to compile and link the receiving program within Developer Studio, select File > Open Workspace..., select filename recvw32m.mak from your tutorial directory, and then select Build > Build receive.

All further examples in this Tutorial will assume that you are familiar with compiling and linking programs as described above.