工厂模式强制用一个通用的工厂（factory）来创建对象，而不允许将创建对象的代码散布于整个系统。如果程序中所有需要创建对象的代码都转到这个工厂执行，那么再增加新对象时的所要做的全部工作就是只需修改工厂。这种设计是众所周知的工厂方法的一种变体。
#include <iostream> #include <stdexcept> #include <cstddef> #include <string> #include <vector> //#include "../purge.h" using namespace std; class Shape { public: virtual void draw() = 0; virtual void erase() = 0; virtual ~Shape() {} class BadShapeCreation : public logic_error { public: BadShapeCreation(string type) : logic_error("Cannot create type " + type) {} }; static Shape* factory(const string& type) throw(BadShapeCreation); }; class Circle : public Shape { Circle() {} // Private constructor friend class Shape; public: void draw() { cout << "Circle::draw" << endl; } void erase() { cout << "Circle::erase" << endl; } ~Circle() { cout << "Circle::~Circle" << endl; } }; class Square : public Shape { Square() {} // Private constructor friend class Shape; public: void draw() { cout << "Square::draw" << endl; } void erase() { cout << "Square::erase" << endl; } ~Square() { cout << "Square::~Square" << endl; } }; Shape* Shape::factory(const string& type) throw(Shape::BadShapeCreation) { if(type == "Circle") return new Circle; if(type == "Square") return new Square; throw BadShapeCreation(type); } char* sl[] = { "Circle", "Square", "Square", "Circle", "Circle", "Circle", "Square" }; int main() { vector<Shape*> shapes; try { for(size_t i = 0; i < sizeof sl / sizeof sl[0]; i++) shapes.push_back(Shape::factory(sl[i])); } catch(Shape::BadShapeCreation e) { cout << e.what() << endl; /* purge(shapes); */ return EXIT_FAILURE; } for(size_t i = 0; i < shapes.size(); i++) { shapes[i]->draw(); shapes[i]->erase(); } /* purge(shapes); */ }在添加新的Shape类型时，函数factory()是当前系统中惟一需要修改的代码。
选自《C++编程思想》。
转载于:https://www.cnblogs.com/chinaxmly/archive/2012/10/01/2709796.html
