Implement shared memory data publishing between nodelets [closed]

edit

I have a set of 3 nodelets running which publish and subscribe to topics amongst themselves. To optimize the process I want to use the shared memory functionality for zero-copy data being shared between nodelets through publish and subscribe. I tried following this example. The example uses a very basic data type for std_msgs::String::ConstPtr. I am using a custom defined message and I get a compile time error saying that I cannot assign values to boost::shared_ptr.

For e.g. if my message type is the following (MyMessage.msg)-

Header header
int dataA
string dataB

In my publish method I do something like this -

void publishTopic()
{
    std::string str("my message");
    MyMessage::ConstPtr msg;
    msg->dataA = 5;
    msg->dataB = str;

    myPublisher.publish(msg);
}

Lines msg->dataA = 5 and msg->dataB = str are giving me the errors. I know I'm doing something wrong with how I'm assigning values to pointers, but cannot think of a solution off the top of my head. Any help will be appreciated.

Can you please also refer a documentation for using boost::shared_ptr in ROS if any exists?