1. Computer Science and Software Engineering University of Wisconsin - Platteville 5. Template Yan Shi CS/SE 2630 Lecture Notes

2. Void Pointer void * p; // Declare like a normal pointer, use the // void keyword as the pointer type.  AKA generic pointer: can be pointed at objects of any data type! int num; float value = 1.2; p = # p = &value; —One of its possible uses may be to pass generic parameters to a function.  cannot be dereferenced! We don’t know the type.. —cast the void pointer before dereference it — cout ( p );  also cannot do pointer arithmetic! same reason.  Avoid using void pointers if possible. There are other ways to achieve genetic functions!

3. Generic  What is the purpose of typedef Fruit InfoType;  To make your operation/data structure more generic, we can use a template function/class.  Template: a C++ language construct that allows the compiler to generate multiple versions of a class type or a function by allowing parameterized type.

4. Function Template  To declare: template function_declaration;  To use: function_name (parameters);  Make sure the operations defined in the function template are defined for the type of objects that are using the template. template Type max(const Type &a, const Type &b) { return a > b ? a : b; } … max ( 5, 9 ); max ( mike, alex );

5. Function Template  In some cases the compiler can automatically find out the type.  We can also define function templates that accept more than one type of parameter: int i,j; max(i,j); template T GetMin (T a, U b) { return ( a < b ? a : b ); } … int i,j; long l; i = GetMin (j,l);

6. Class Template template class Stack { protected: int height; ItemType items[50]; public: Stack() : height(0) { } void push(ItemType x) { items[height] = x; ++height; } ItemType pop() { height--; return items[height]; } bool isEmpty() const { return height <= 0; } bool isFull() const { return height >= 50; } }; Stack stuStack; Stack nums; nums.push(10);

7. Template Class  At compile time, the compiler generates distinct class types and gives its own internal name to each type. — Stack_Student stuStack; — Stack_int nums;  The new class types are called template classes.  Similar to template functions.

8. Implementing Class Template  Two options: —put all code for template in.h file //preferred! —in the implementation file, precede the member function definition with the template prefix  An implementation trick: —drive template class from non-template class, put most code in base class template void Stack ::push(ItemType x) { items[height] = x; ++height; } class ComplexContainer {... }; template class Container : public ComplexContainer {...};

9. Non-Type Parameters  Can also have multiple type parameters: template class Stack { protected: int height; ItemType items[size]; public: Stack() : height(0) { } void push(ItemType x) { items[height] = x; ++height; } ItemType pop() { height--; return items[height]; } bool isEmpty() const { return height <= 0; } bool isFull() const { return height >= size; } } … Stack st;

10.  Type checking is guaranteed when using class templates  Solution: make DoIt a function template! Type Checking void DoIt(Stack chs) {…} Stack letters; letters.push(“something”); //illegal! DoIt(letters); //illegal! template void DoIt(Stack stack) {…} Stack letters; DoIt(letters); //OK!

11. inline Function  keyword inline : function is treated as a macro inline template T sqr(const T &x) { return x * x; } the preprocessor converts the code cout << sqr(5); into cout << 5 * 5;  Pros: —no function call overhead —compiler optimization  Cons: —Expand code if inline function is long —hard to debug: it looks like a function is being called, but it's not really  inline functions should only be in header files! —compiler must see body of inline function to do the job.  class members defined within class definition are automatically inlined.