C++ Functions, Classes, and Templates C++ functions encapsulate behavior Data used/modified by a function must be passed in via parameters Data produced by a function must be passed out via return type Classes (and structs) encapsulate related data and behavior Member variables maintain each object’s state Member functions (methods) and operators have direct access to member variables Templates are used to make classes/structs/functions generic For example, vector class template can hold different data types For example, sort algorithm works with different containers as well

Declaring, Defining, Calling C++ Functions // function declarations in myfile.h void foo (); void baz (int j); // function definitions in myfile.cpp void baz (int j){ cout << j << endl; // prints passed value } void foo (){ int i = 7; // foo calls baz, passing variable i to it baz (i);

Declaring, Defining, Using C++ Structs/Classes // declaration (in Point2d.h) struct Point2D { Point2D (int x, int y); bool operator< (const Point2D &) const; int x_; int y_; }; // definitions (in Point2d.cpp) Point2D::Point2D (int x, int y) : x_(x), y_(y) {} bool Point2D::operator< (const Point2D & p2d) const { return (x_ < p2d.x_) || ((x_ == p2d.x_) && (y_ < p2d.y_)); } promises not to modify object on which it’s called base class/struct and member initialization list scoping operator

Using C++ Struct/Class Templates (with Structs) // using standard library code #include <vector> using namespace std; // using user-defined code #include “point2d.h” // main function definition int main (int, char *[]) { vector<Point2D> v; // must give a type here v.push_back(Point2D(2,3)); v.push_back(Point2D(1,4)); return 0; }

Using C++ Function Templates (STL Algorithms) // same as before, and add algorithm library #include <vector> #include <algorithm> using namespace std; #include “point2d.h” int main (int, char *[]) { vector<Point2D> v; v.push_back(Point2D(2,3)); v.push_back(Point2D(1,4)); // reorders the points in the vector // note that you don’t give a type here! sort (v.begin(), v.end()); return 0; }

Another Useful STL Algorithm #include <string> #include <iostream> #include <algorithm> using namespace std; int main (int argc, char * argv[]) { if (argc != 2) { cout << “usage: ” << argv[0] << “ <string>” << endl; return -1; } string s(argv[1]), t(argv[1]); do { next_permutation(s.begin(), s.end()); cout << s << endl; } while (s != t); return 0;