C++ Part 2

Templates

Function Template

int cube(int x) { return x*x*x;}    cube(5.5) ->fails as works with int

Solution: copy function and change its type. Need to do same as we expect different data type cube, long, double etc.

Using template, need just one copy of cube(). When function invoked, T is replaced with specified type during call.

template <typename T>

T cube(T x){return x*x*x;}

cube<int>(5);   cube<double>(5.5)

Datatype need not be specified, compiler can interpret from passed argumentJ.

Side Effect: even though there is one copy, but all occupy different space in final image.

Class Template

template <typename T>

class Vector{

        T arr[100]; int size;

public:

        Vector():size(0) {}

        void push(T x){ arr[size]=x; size++; }

        void print() const {for(int itr=0; itr<size; itr++) cout<<arr[itr]<<endl;}

        int getsize() const{return size;}

        T get(int i) const{return arr[i];}

};

int main(){ Vector<int> v;  v.push(2); v.push(3); v.print(); }

Function template can infer data type from argument, for class template data type should be specifically specified.

Class template with function Template

template <typename T>

Vector<T> operator*(const Vector<T>& a, const Vector<T>& b) {

  Vector<T> ret;

  for(int i=0;i<a.getsize();i++)

        ret.push(a.get(i) *b.get(i) );

  return ret; }

int main(){

        Vector<int> v;    v.push(2); v.push(3); v.push(10); v.print();

        v=cube(v);          v.print();   //v={8, 27, 1000}

}

References
C++ Standard Library by Bo Qian