ROS_INFO_STREAM lack of operator overload?
I am writing a callback function which subscribes to multiple topics. In the callback, i am unable to print console certain structs and it is puzzling. Shouldn't the operators be overloaded already? I am getting the error
error: no match for ‘operator<<’ (operand types are ‘std::basic_ostream<char>’ and ‘const _data_type {aka const std::vector<unsigned char="">}’)
static void callback(const sensor_msgs::PointCloud2ConstPtr& sub1_ptr,const sensor_msgs::PointCloud2ConstPtr& sub2_ptr, const sensor_msgs::PointCloud2ConstPtr& sub3_ptr, const sensor_msgs::PointCloud2ConstPtr& sub4_ptr){
ROS_INFO_STREAM("1st"<< sub1_ptr->data);
ROS_INFO_STREAM("2nd"<< sub2_ptr->data);
ROS_INFO_STREAM("3rd"<< sub3_ptr);
ROS_INFO_STREAM("4th"<< sub4_ptr); }
So basically a pointer (just an address) can be printed, no surprise there. But why can't i print something like a PointCloud2.data? And also, ROS_INFO is the c version of the ros print console function but would it be easier to print something compared to ROS_INFO_STREAM?
C++ doesn't have any overload for
<<forstd::vector<T>by default. That's not ROS specific, but C++.What made you assume such an overload should be provided?
It feels right for ROS to provide certain functionalities to go along with ROS_INFO_STREAM. After all, the things we will print to console would likely be visualisation of ROS data, especially the data structs. It is like coming up with a new coffee machine that makes a new type of coffee but you have to make the gears inside yourself. Anyways, i could write the overload myself for sure but that would assume i understand the data and a quick way to understand the data would be to print it out to console but i cannot do that in such a case. So yeah.
It's probably pedantic, but a
std::vector<unsigned char>is not "a ROS data struct". It's a plain C++ STL type.There are typically overloads for ROS message types, but that's not what you're passing to
ROS_INFO_STREAM(..)in your example.According to sensor_msgs/PointCloud2, the
datafield is auint8[], which is mapped to astd::vector<unsigned char>.std::to_string(..)still doesn't support that, so you'd have to implement that yourself, yes.