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The problem is with your subscription callback signature. In Foxy, std::function<void (const std::shared_ptr<const MessageT> &)> (what you have) is not a supported signature for a subscription callback.

The list of supported subscription callbacks in Foxy is (reference: https://docs.ros2.org/foxy/api/rclcpp/classrclcpp_1_1AnySubscriptionCallback.html)

• std::function<void (std::unique_ptr<MessageT, MessageDeleter>)>
• std::function<void (std::unique_ptr<MessageT, MessageDeleter>, const rclcpp::MessageInfo &)>
• std::function<void (const std::shared_ptr<const MessageT>)>
• std::function<void (const std::shared_ptr<const MessageT>, const rclcpp::MessageInfo &)>
• std::function<void (std::shared_ptr<MessageT>)>
• std::function<void (std::shared_ptr<MessageT>, const rclcpp::MessageInfo &)>

The quick fix here would be to drop the reference to the message's constant shared_ptr, instead opting to just receive a constant shared_ptr in your subscription callback as such:

void cmd_dirCallback(const std_msgs::msg::String::SharedPtr msg);