unidentified reference issue when having .h and .cpp files

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Hi everyone, I am trying to have .h and .cpp files in my ros package. All my code is in the src file and I have the following code. The code works fine when I run through xcode so the syntax is okay however ros does not like it for some unknown reason: Here is the .h file

#include <iostream>
class DroneCommands{

public:

DroneCommands();
void Land(int time);



 };
  #endif /* defined(__helloworld__DroneCommands__) */

Here is the .cpp file:

#include "DroneCommands.h"
#include <iostream>


DroneCommands::DroneCommands(){
std::cout << "object created" << std::endl;
}




void DroneCommands::Land(int time){
std::cout << "Landing!!" << std::endl;

}

Finally, here is main.cpp: #include <iostream> #include "DroneCommands.h"

int main(int argc, char **argv)
{
DroneCommands dc; 
dc.Land(3);

}

The command prompt error is: undefined reference to `DroneCommands::DroneCommands()'

Please let me know why this does not work even though I can get it to run on Xcode successfully. Thanks :)