// classes and uniform initialization
#include <iostream>
using namespace std; class Circle {
double radius;
public:
Circle(double r) { radius = r; }
double circum() {return 2*radius*3.14159265;}
}; int main () {
Circle foo (10.0); // functional form
Circle bar = 20.0; // assignment init.
Circle baz {30.0}; // uniform init.
Circle qux = {40.0}; // POD-like cout << "foo's circumference: " << foo.circum() << '\n';
cout << "bar circumference: " << bar.circum() << '\n';
cout << "bazcircumference: " << baz.circum() << '\n';
cout << "qux circumference: " << qux.circum() << '\n';
return 0;
}
Rectangle rectb; // default constructor called
Rectangle rectc(); // function declaration (default constructor NOT called)
Rectangle rectd{}; // default constructor called
Member initialization in constructors
When a constructor is used to initialize other members, these other members can be initialized directly, without resorting to statements in its body. This is done by inserting, before the constructor's body, a colon (:) and a list of initializations for class members. For example, consider a class with the following declaration:
class Rectangle {
int width,height;
public:
Rectangle(int,int);
int area() {return width*height;}
};
The constructor for this class could be defined, as usual, as:
Rectangle::Rectangle (int x, int y) { width=x; height=y; }
But it could also be defined using member initialization as:
Rectangle::Rectangle (int x, int y) : width(x) { height=y; }
Or even:
Rectangle::Rectangle (int x, int y) : width(x), height(y) { }
Note how in this last case, the constructor does nothing else than initialize its members, hence it has an empty function body.