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Implement shared memory data publishing between nodelets [closed]

asked 2014-12-23 13:05:20 -0500

ajain gravatar image

updated 2014-12-23 17:05:24 -0500

tfoote gravatar image

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;


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?

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Closed for the following reason the question is answered, right answer was accepted by ajain
close date 2015-01-05 12:40:03.792973

1 Answer

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answered 2014-12-23 17:12:46 -0500

tfoote gravatar image

Your problem is that you're using const pointers. const pointers cannot be mutated, which is why you are getting errors.

When you are generating a message for publishing it needs to be a standard shared pointer. When you receive it in your callback it will be a const pointer or else it will be copied.

Note: When you publish a message with a shared pointer you're not allowed to modify it after it has been sent as other parts of the process might be accessing it.

For information on boost pointers I suggest the boost documentation: Or general reference sites like stack overflow:

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Thanks a lot for a quick answer. It works if I instantiate msg as boost::shared_ptr<MyMessage> msg.

ajain gravatar image ajain  ( 2014-12-23 18:01:01 -0500 )edit

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Asked: 2014-12-23 13:05:20 -0500

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Last updated: Dec 23 '14