Templates

C++ 2 Outline Function templates  Function template definition  Function template overloading Class templates  Class template definition  Class template objects

C++ 3 Function templates  If we would like to define a function in such a way as we should call it for different types of parameters, we can define a function template.  This template contains template parameters which will be substituted with real types, when calling the function.

C++ 4 Function Template Definition  We start the function definition with template where the list of parameters must be given in the form: class name_1, class name_2,..., class name_n  Thus, name_i can substitute a type.  The list of formal parameters of the function must contain all type parameters.

C++ 5 Example #include using namespace std; template void MySwap(T& a, T& b) { T x; x = a; a = b; b = x; }

C++ 6 The Print_Swap Function template void Print_Swap(T& a, T& b) { cout << "before swapping:\n"; cout << "a =" << a << "\t"; cout << "b =" << b << endl;

C++ 7 The Print_Swap Function MySwap(a, b); cout << "after swapping:\n"; cout << "a =" << a << "\t"; cout << "b =" << b << endl; }

C++ 8 The main Function int main() { int u = 3; int v = 5; Print_Swap(u, v); double y = 3.2; double z = 5.7; Print_Swap(y, z); }

C++ 9 Output before swapping: a =3 b =5 after swapping: a =5 b =3 before swapping: a =3.2 b =5.7 after swapping: a =5.7 b =3.2

C++ 10 Example 2 #include using namespace std; template void Display_Type(T a) { cout << a << "\t"; cout << typeid(T).name() << endl; }

C++ 11 The Fraction Class class Fraction { int numerator; int denominator; public: Fraction(int a, int b); ostream& Display(ostream &s) const; };

C++ 12 Constructor Fraction::Fraction(int a, int b) { numerator = a; denominator = b; }

C++ 13 The Display Function ostream& Fraction::Display(ostream &s) const { return s << numerator << " / " << denominator; }

C++ 14 Inserter Operator Overloading ostream& operator <<(ostream& s, const Fraction & t) { return t.Display(s); }

C++ 15 The main Function int main() { Display_Type(3); Display_Type(5.9); Fraction y(4, 9); Display_Type(y); }

C++ 16 Output 3 int 5.9 double 4 / 9 class Fraction

C++ 17 Function Template Overloading  If we don’t want to generate an issue of the function template for a specific list of parameters, then we can overload the function template.  This should be done by adding a conventional function to the code, which has exactly the required list of parameters.

C++ 18 Example (MySwap) #include using namespace std; //...

C++ 19 MySwap template void MySwap(T& a, T& b) { T x; x = a; a = b; b = x; cout << "With function template\n"; }

C++ 20 Allow Different Types template void Print_Swap(T1& a, T2& b) { cout << "before swapping:\n"; cout << "a =" << a << "\t"; cout << "b =" << b << endl; MySwap(a, b); cout << "after swapping:\n"; cout << "a =" << a << "\t"; cout << "b =" << b << endl; }

C++ 21 Overloading void MySwap(int& a, double& b) { int x; x = a; a = static_cast (b); b = x + fabs(b-a); cout << "Without a template\n"; }

C++ 22 The main function void main() { double y = 3.2; double z = 5.7; Print_Swap(y, z); int t = 7; double w = 10.9; Print_Swap(t, w); }

C++ 23 Output before swapping: a =3.2 b =5.7 With function template after swapping: a =5.7 b =3.2 before swapping: a =7 b =10.9 Without a template after swapping: a =10 b =7.9 Change only integer parts

C++ 24 Class Template Definition  Definition: template class ClassName { //... };  The list of parameters can contain type parameters and constant parameters.  The type parameters should be given in the form class name and the constant parameters as an ordinary declaration, in the form type name.

C++ 25 Member Function Definition  If the member functions are defined outside the class, then these should be function templates.  Thus, they should start with: template  After the class name we should give only the parameter names between the signs.

C++ 26 Example (member function) template class MyStack { T t[I]; public: //... void Push(T x); }; template void MyStack ::Push(T x){ //... }

C++ 27 Objects of the Class Template  When defining an object, after the class name one has to give the type parameters and the constant parameters.  Use the following form: classname object;  Example: MyStack v;

C++ 28 Example  Define the MyStack class template, with the Push and Pop member functions, and overload the inserter << operator such that all the elements should be take out from the stack. #include using namespace std;

C++ 29 The MyStack Class Template template class MyStack { T t[I]; int n; public: class FullStack {}; // exception

C++ 30 The MyStack Class Template class EmptyStack{}; //exception MyStack() { n = 0; } void Push(T x); T Pop(); ostream& Pop_Print(ostream& s); };

C++ 31 The Push Member Function template void MyStack ::Push(T x) { if ( n == I ) throw FullStack(); t[n++] = x; }

C++ 32 The Pop Member Function template T MyStack ::Pop() { if ( n == 0 ) throw EmptyStack(); return t[--n]; }

C++ 33 The Pop_Print Member Function template ostream& MyStack ::Pop_Print (ostream& s) { while(n > 0) s << t[--n] << " "; return s << endl; }

C++ 34 The Inserter Operator template ostream& operator & v) { return v.Pop_Print(s); }

C++ 35 The first main function (10 elements of type int) int main() { const int dim = 10; MyStack v; for(int i = 0; i < dim; i++) v.Push(i); cout << v; } Output:

C++ 36 The second main function (5 elements of type double) int main() { const int dimension = 5; MyStack v2; for(int i = 0; i < dimension; i++) v2.Push(i + static_cast (i) / 10); cout << v2; } Output:

C++ 37 The third main function (full stack) int main() { const int dim = 10; MyStack v; try { for(int i = 0; i <= dim; i++) v.Push(i); } catch( MyStack ::FullStack ) { cout << "The stack is full.\n"; } The stack is full. Output:

C++ 38 The last main function (empty stack) int main() { const int dim = 10; MyStack v; for(int i = 0; i < dim; i++) v.Push(i); try { while( true)cout << v.Pop() << " "; } catch( MyStack ::EmptyStack ) { cout << "Empty.\n"; } Empty. Output: