CoreDX DDS Hello World Example in C++
Here is a 'C++' CoreDX DDS version of the typical "Hello World" application.
This example consists of two applications: one application that publishes a simple string message Topic (the data contains the string "hello world!"); and one application that subscribes to this topic.
The source code presented here is the 'C++' programming language version of the 'hello world' applications. It can interoperate with 'hello world' applications written in other languages, or running on different hardware platforms.
file: hello.ddl
struct StringMsg
{
string msg;
};
file: hello_pub.cc
/****************************************************************
*
* file: hello_pub.c
* desc: Provides a simple C++ 'hello world' DDS publisher.
* This publishing application will send data
* to the example 'hello world' subscribing
* application (hello_sub).
*
****************************************************************
*
* This file is provided by Twin Oaks Computing, Inc
* as an example. It is provided in the hope that it will be
* useful but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
* PURPOSE. TOC Inc assumes no liability or responsibilty for
* the use of this information for any purpose.
*
****************************************************************/
#include <stdio.h>
#include <string.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
#include <dds/dds.hh>
#include "hello.hh"
#include "helloTypeSupport.hh"
#include "helloDataWriter.hh"
/****************************************************************
* main()
*
* Perform CoreDX DDS setup activities:
* - create a Domain Participant
* - create a Publisher
* - register the StringMsg data type
* - create a Topic
* - create a DataWriter
* Write data
****************************************************************/
int main(int argc, char * argv[])
{
DomainParticipant * domain;
Publisher * publisher;
Topic * topic;
DataWriter * dw;
StringMsg stringMsg;
ReturnCode_t retval;
class DomainParticipantFactory * dpf =
DomainParticipantFactory::get_instance();
/* create a DomainParticipant */
domain = dpf->create_participant( 0,
PARTICIPANT_QOS_DEFAULT,
NULL,
0 );
if ( domain == NULL )
{
printf("ERROR creating domain participant.\n");
return -1;
}
/* create a Publisher */
publisher = domain->create_publisher(PUBLISHER_QOS_DEFAULT,
NULL,
0 );
if ( publisher == NULL )
{
printf("ERROR creating publisher.\n");
return -1;
}
/* Register the data type with the CoreDX middleware.
* This is required before creating a Topic with
* this data type.
*/
StringMsgTypeSupport stringMsgTS;
retval = stringMsgTS.register_type( domain, NULL );
if (retval != RETCODE_OK)
{
printf("ERROR registering type\n");
return -1;
}
/* Create a DDS Topic with the StringMsg data type. */
topic = domain->create_topic("helloTopic",
"StringMsg",
TOPIC_QOS_DEFAULT,
NULL,
0 );
if ( topic == NULL )
{
printf("ERROR creating topic.\n");
return -1;
}
/* Create a DataWriter on the hello topic, with
* default QoS settings and no listeners.
*/
dw = publisher->create_datawriter( topic,
DATAWRITER_QOS_DEFAULT,
NULL,
0 );
if (dw == NULL)
{
printf("ERROR creating data writer\n");
return -1;
}
/* Initialize the data to send. The StringMsg data type
* has just one string member.
* Note: Alwyas initialize a string member with
* allocated memory -- the destructor will free
* all string members.
*/
stringMsg.msg = new char[strlen("Hello WORLD from C++!")+1];
strcpy(stringMsg.msg, "Hello WORLD from C++!");
while ( 1 )
{
ReturnCode_t ret = dw->write ( &stringMsg, HANDLE_NIL );
printf("wrote a sample\n");
fflush(stdout);
if ( ret != RETCODE_OK)
{
printf("ERROR writing sample\n");
return -1;
}
#ifdef _WIN32
Sleep(1000);
#else
sleep(1);
#endif
}
/* Cleanup */
retval = domain -> delete_contained_entities();
if ( retval != DDS_RETCODE_OK )
printf("ERROR (%s): Unable to cleanup DDS entities\n",
DDS_error(retval));
return 0;
}
file: hello_sub.cc
/****************************************************************
*
* file: hello_sub.c
* desc: Provides a simple C++ 'hello world' DDS subscriber.
* This subscribing application will receive data
* from the example 'hello world' publishing
* application (hello_pub).
*
****************************************************************
*
* This file is provided by Twin Oaks Computing, Inc
* as an example. It is provided in the hope that it will be
* useful but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
* PURPOSE. TOC Inc assumes no liability or responsibilty for
* the use of this information for any purpose.
*
****************************************************************/
#include <stdio.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
#include <dds/dds.hh>
#include "hello.hh"
#include "helloTypeSupport.hh"
#include "helloDataReader.hh"
#ifdef _WIN32
# define SLEEP(a) Sleep(a*1000)
#else
# define SLEEP(a) sleep(a);
#endif
int all_done = 0;
/****************************************************************
* Construct a DataReaderListener and override the
* on_data_available() method with our own. All other
* listener methods will be default (no-op) functions.
****************************************************************/
class SubListener : public DataReaderListener
{
public:
void on_data_available( DataReader * dr );
};
/****************************************************************
* DataReader Listener Method: on_data_avail()
*
* This listener method is called when data is available to
* be read on this DataReader.
****************************************************************/
void SubListener::on_data_available( DataReader * dr)
{
StringMsgPtrSeq samples;
SampleInfoSeq samples_info;
ReturnCode_t retval;
SampleStateMask ss = DDS_ANY_SAMPLE_STATE;
ViewStateMask vs = DDS_ANY_VIEW_STATE;
InstanceStateMask is = DDS_ANY_INSTANCE_STATE;
/* Convert to our type-specific DataReader */
StringMsgDataReader * reader = StringMsgDataReader::narrow( dr );
/* Take any and all available samples. The take() operation
* will remove the samples from the DataReader so they
* won't be available on subsequent read() or take() calls.
*/
retval = reader->take( &samples, &samples_info,
LENGTH_UNLIMITED,
ss,
vs,
is );
if ( retval == RETCODE_OK )
{
/* iterrate through the samples */
for ( unsigned int i = 0;i < samples.size(); i++)
{
/* If this sample does not contain valid data,
* it is a dispose or other non-data command,
* and, accessing any member from this sample
* would be invalid.
*/
if ( samples_info[i]->valid_data)
printf("Sample Received: msg %d = %s\n", i,
samples[i]->msg);
}
fflush(stdout);
/* read() and take() always "loan" the data, we need to
* return it so CoreDX can release resources associated
* with it.
*/
reader->return_loan( &samples, &samples_info );
}
else
{
printf("ERROR (%s) taking samples from DataReader\n",
DDS_error(retval));
}
}
/****************************************************************
* main()
*
* Perform CoreDX DDS setup activities:
* - create a Domain Participant
* - create a Subscriber
* - register the StringMsg data type
* - create a Topic
* - create a DataReader and attach the listener created above
* And wait for data
****************************************************************/
#if defined(__vxworks) && !defined(__RTP__)
int hello_sub(char * args)
#else
int main(int argc, char * argv[])
#endif
{
DomainParticipant * domain;
Subscriber * subscriber;
Topic * topic;
DataReader * dr;
SubListener drListener;
ReturnCode_t retval;
/* Get an instance of the DDS DomainPartiticpantFactory --
* we will use this to create a DomainParticipant.
*/
DomainParticipantFactory * dpf =
DomainParticipantFactory::get_instance();
/* create a DomainParticipant */
domain =
dpf->create_participant( 0,
PARTICIPANT_QOS_DEFAULT,
NULL,
0 );
if ( domain == NULL )
{
printf("ERROR creating domain participant.\n");
return -1;
}
/* create a Subscriber */
subscriber = domain->create_subscriber(SUBSCRIBER_QOS_DEFAULT,
NULL,
0 );
if ( subscriber == NULL )
{
printf("ERROR creating subscriber\n");
return -1;
}
/* Register the data type with the CoreDX middleware.
* This is required before creating a Topic with
* this data type.
*/
StringMsgTypeSupport stringMsgTS;
retval = stringMsgTS.register_type( domain, NULL );
if (retval != RETCODE_OK)
{
printf("ERROR (%s) registering type\n", DDS_error(retval));
return -1;
}
/* create a DDS Topic with the StringMsg data type. */
topic = domain->create_topic( "helloTopic",
"StringMsg",
TOPIC_QOS_DEFAULT,
NULL,
0 );
if ( ! topic )
{
printf("ERROR creating topic\n");
return -1;
}
/* create a DDS_DataReader on the hello topic (notice
* the TopicDescription is used) with default QoS settings,
* and attach our listener with our on_data_available method.
*/
dr = subscriber->create_datareader( (TopicDescription*)topic,
DATAREADER_QOS_DEFAULT,
&drListener,
DATA_AVAILABLE_STATUS );
if ( ! dr )
{
printf("ERROR creating data reader\n");
return -1;
}
/* Wait forever. When data arrives at our DataReader,
* our dr_on_data_avilalbe method will be invoked.
*/
while ( !all_done )
SLEEP(30);
/* Cleanup */
retval = domain -> delete_contained_entities();
if ( retval != DDS_RETCODE_OK )
printf("ERROR (%s): Unable to cleanup DDS entities\n",
DDS_error(retval));
return 0;
}