Template functions and classes in C++ allow functions and classes to operate on multiple data types rather than a single data type. The document discusses how template functions define a type parameter to replace the data type, and template classes define member functions and variables as templates. It provides examples of template functions used in ROS for message passing, including advertise and subscribe, which allow publishing and subscribing to messages of different types.

1. -Eric Cote TEMPLATE FUNTIONS/CLASSES IN C++ AND LAB 1: INTRODUCTION TO ROS MESSAGE PASSING

2. Template Functions -What if you need the same function for two different variable types?

3. void swap_values(char& v1, char& v2) { char temp; temp = v1; v1 = v2; v2 = temp; }

4. void swap_values(int& v1, int&v2) { int temp; temp = v1; v1 = v2; v2 = temp; }

5. template<class T> void swap_values(T& v1, T& v2) { T temp; temp = v1; v1 = v2; v2 = temp; } Instead, Let's Use a Template!

6. template<class T> void swap_values(T& v1, T& v2) { T temp; temp = v1; v1 = v2; v2 = temp; } (Type) Type Parameter Type Parameter to be replaced

7. template<class T> void swap_values(T& v1, T& v2) { T temp; temp = v1; v1 = v2; v2 = temp; } int main() { int integer1 = 1, integer 2 = 2; swap_values(integer1, integer2); cout << “integer1 now equals ” << integer1 << endl; cout << “integer2 now equals ” << integer2 << endl; return 0; }

8. Template Classes: A Brief Class Refresher class Robot { public: void funktion1(); private: void funktion2(); int v1; int v2; };

9. class Robot { public: void funktion1(); private: void funktion2(); int v1; int v2; }; Class Name Public Member Function Private Variables and Member Functions

10. class Robot { … } void Robot::funktion2(); { ... } Scope Resolution Operator

11. class Robot { public: void funktion1(); private: void funktion2(); int v1; int v2; }; class Robot { public: void funktion1(); private: void funktion2(); char v1; char v2; }; What if We Want?

12. Time for a Template Class template<class T> class Robot { public: void funktion1(T v1, T v2); private: void funktion2(); T v1; T v2; };

13. template<class T> class Robot { ... }; template<class T> void Robot<T>::funktion1(T v1, T v2); { v1 = v2; } Member Functions Are Also Templates Scope Resolution Operator

14. Do All the Variables in the Class Need to be of Type T? template<class T> class Robot { public: void funktion1(int v1, T v2); private: void funktion2(); int v1; T v2; }; Data Types to be Given by User

15. Using the Template Function int main() { Robot<char> robot1; Robot<double> robot2; }

16. Template Functions in Lab 1 n.advertise<std_msgs::String>(&quot;chatter&quot;, 1000); n.subscribe(&quot;chatter&quot;, 1000, chatterCallback);

17. In talker.cpp ros::Publisher chatter_pub = n.advertise<std_msgs::String>(&quot;chatter&quot;, 1000); #1 A Template Function! Scope Resolution Operator

18. n.advertise<std_msgs::String>(&quot;chatter&quot;, 1000); Parameter 1 Parameter 2 Scope Resolution Operator

19. ros::Subscriber chatter_sub = n.subscribe(&quot;chatter&quot;, 1000, chatterCallback); In listener.cpp Another Template Function! Why no <type>?

20. n.subscribe(&quot;chatter&quot;, 1000, chatterCallback); Parameter 1 Parameter 2

21. Other Things to Know for Lab1 -The dot operator object.memberfunction -Pointer operations -> and char** object * 0; (*0).dosomething; == 0->dosomething; -Unary ++ operator -argc and argv

22. Acknowledgements -Professor Main -Problem Solving with C++ by Walter Savitch—The template function example came from this book. -ROS.org -Sam

23. Questions?