I'm defining a class SpatialCriterionCallback in a header file "spatialcriterion.h" like this:
#include "ros/ros.h"
#include "neuromorphic_stereo/MatchingCandidates.h"
#include <vector>
class SpatialCriterionCallback
{
public:
// constructors & destructors
SpatialCriterionCallback()=default;
SpatialCriterionCallback(ros::NodeHandle);
~SpatialCriterionCallback()=default;
private:
std::vector<neuromorphic_stereo::MatchingCandidates> matching_candidates;
void subscriberCallbackFunction(constneuromorphic_stereo::MatchingCandidates&);
}
Then in the file "spatialcriterion.cpp" I'm defining a constructor that invokes a ros::SubscriberNode like this:
#include "spatialcriterioncallback.h"
SpatialCriterionCallback::SpatialCriterionCallback(ros::NodeHandle n)
{
this->n =n;
this->time_criterion_topic_handle = this->n.subscribe("TimeCriterionTopic",
1e4,
&SpatialCriterionCallback::subscriberCallbackFunction,
this);
}
When I try compiling this within a qtcreator project, the compiler tells me
error: undefined reference to `SpatialCriterionCallback::subscriberCallbackFunction(neuromorphic_stereo::MatchingCandidates_ const&)'
When I add the following lines to my "spatialcriterion.cpp" file it will compile just fine:
void SpatialCriterionCallback::subscriberCallbackFunction(const neuromorphic_stereo::MatchingCandidates & msg){
this->matching_candidates.push_back(msg);
}
Now my question is: Shouldn't this code compile without the function definition, because the function subscriberCallbackFunction() has already been declared in "spatialcriterion.h"? Why is it necessary for the compiler to have the function defined?
I also tried finding an explanation to this behaviour here, but all the other posts about failing forward declaration (like this or this) aren't exactly what I'm looking for.
Even if you declared the method in your class, it doesn't exist.
When you reference that function in the constructor, the linker tells you that it needs to know where the method is.
The code compiles fine, it doesn't link.