C++构造函数使用的多种方法

冷不防 2021-11-02 07:20 365阅读 0赞

// 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.

转载于:https://www.cnblogs.com/CodeWorkerLiMing/p/11074537.html