Chapter 17 Templates

Generic Algorithms Algorithms in which the actions or steps are defined, but the data types of the items being manipulated are not.

Examples Of Generic Algorithm Swap the values of two variables of the same data types Find the index of the smallest value in an array. Pair up 2 values Linked list

Overloading functions for Generic Algorithms void swap (char& v1, char& v2) { char temp = v1; v1 = v2; v2 = v3; } void swap (int& v1, int& v2) { int temp = v1; v1 = v2; v2 = v3; } void double (double & v1, double & v2) { double temp = v1; v1 = v2; v2 = v3; } void swap (CAny& v1, CAny& v2) { CAny temp = v1; v1 = v2; v2 = v3; }

Template for Functions template void swap (T& v1, T& v2) { T temp = v1; v1 = v2; v2 = v3; } int main () { int i1=1, i2=2; swap (i1, i2); char c1=‘a’, c2=‘A’; swap (c1, c2); }

Template Function Notes The words template tell the compiler this is a template for a generic data type T and that T is the parametized type which can be replaced by a defined data type. T must have all of the operations used in the template function. int a[5], b[5]; … // Some code to fill up arrays swap (a, b); // NO! There is no assignment operator for arrays

Class Template //Class template for a pair of values of type T template class Pair { public: Pair(); Pair(T f, T s); void setElement (int pos, T val); T getElement (int pos); private: T first; T second; };

Class Template (cont.) template Pair ::Pair() {} template Pair ::Pair(T f, T s) { first = f; second = s; } template void Pair ::setElement (int pos, T val) { if (pos == 1) first = val; else second = val; } template T Pair ::getElement (int pos) { if (pos == 1) return first; else return second; } void main () { Pair scores; Pair seats(‘A’, ‘B’); score.setElement(1, 3); score.setElement(2, 5); char mySeat mySeat=seats.getElement(1); }

Class Template Notes The words template tell the compiler this is a template for a generic data type T and that T is the parametized type which can be replaced by a defined data type. T is used as a type in all function definitions or parameters of the class template. You can use typedef to improve readability. typedef Pairs PairsOfInt; then declare PairsOfInt score; Type T is specialized by giving a type argument to the class name in place of the T.