ROS2 Message Serialization to String in C++

Question

I have a simple subscriber to a topic in C++, and am receiving a custom PositionMsg, which includes other custom messages (Velocity, datum, etc). ROS2 handles all that very well, I'm getting the information.

Now I have been told to serialize the message as a string and store it in a database, where it will need to be deserialized later. Is there something in ROS2 that can write it out as a string. I can use Serialization and get back a SerializedMessage, but how do I save that as a std::string? It does not need to be easily human readable as a string, but if it is easier to do in yaml or json, that is fine too.

Answer 1

I think this is just an array to string problem, there's an array of uint8_t inside the SerializedMessage wrapper:

auto message = std_msgs::msg::String();
message.data = "Hello, world!"; 

rclcpp::Serialization<std_msgs::msg::String> stringSerializer;
rclcpp::SerializedMessage serialized_msg;
stringSerializer.serialize_message(&message, &serialized_msg);
const auto buffer_begin = serialized_msg.get_rcl_serialized_message().buffer;
const auto buffer_end = buffer_begin + serialized_msg.size();
std::string serialized_msg_str(buffer_begin, buffer_end);

https://stackoverflow.com/questions/17982752/convert-vector-of-uint8-to-string and also using https://stackoverflow.com/questions/77315367/how-to-implement-deserialization-of-ros2-messages