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网站可以不备案吗,网站建设与维护的选择题,天津建设网网站打不开,农产品大宗交易平台基本原理#xff1a;CRTP#xff08;Curiously Recurring Template Pattern#xff09;是一种 C 编程设计模式#xff0c;类似于 RAII、SFINAE、这些东西。核心思想只有一个东西#xff1a;即派生类继承以自身为模板参数的基类模板#xff0c;这样子呢#xff0c;在 C 编…基本原理CRTPCuriously Recurring Template Pattern是一种 C 编程设计模式类似于 RAII、SFINAE、这些东西。核心思想只有一个东西即派生类继承以自身为模板参数的基类模板这样子呢在 C 编译替换期间时它可以知道模版类型信息的所以可以调用目标的成员函数。不带虚函数用途一#include iostream #include vector #include cmath #include memory #include iomanip #include variant // CRTP 基类模板不继承任何虚基类完全静态多态 template typename Derived class Shape { public: double area() const { return static_castconst Derived*(this)-calculateArea(); } double perimeter() const { return static_castconst Derived*(this)-calculatePerimeter(); } void printInfo() const { std::cout std::fixed std::setprecision(2) Area: area() , Perimeter: perimeter() \n; } }; // 圆形 class Circle : public ShapeCircle { double radius; public: Circle(double r) : radius(r) {} double calculateArea() const { return M_PI * radius * radius; } double calculatePerimeter() const { return 2 * M_PI * radius; } }; // 矩形 class Rectangle : public ShapeRectangle { double width, height; public: Rectangle(double w, double h) : width(w), height(h) {} double calculateArea() const { return width * height; } double calculatePerimeter() const { return 2 * (width height); } }; // 三角形 class Triangle : public ShapeTriangle { double a, b, c; public: Triangle(double s1, double s2, double s3) : a(s1), b(s2), c(s3) {} double calculateArea() const { double s (a b c) / 2; return std::sqrt(s * (s - a) * (s - b) * (s - c)); } double calculatePerimeter() const { return a b c; } }; // 使用 std::variant 存储不同类型的形状实现类型安全的统一处理 using ShapeVariant std::variantCircle, Rectangle, Triangle; // Visitor 用于调用 printInfo struct PrintVisitor { templatetypename T void operator()(const T shape) const { shape.printInfo(); } }; int main() { // 创建形状对象并存储在 std::variant 向量中 std::vectorShapeVariant shapes; shapes.emplace_back(Circle(5.0)); shapes.emplace_back(Rectangle(4.0, 6.0)); shapes.emplace_back(Triangle(3.0, 4.0, 5.0)); std::cout 使用 std::variant 和 Visitor 统一处理无虚函数调用:\n; for (const auto shape : shapes) { std::visit(PrintVisitor{}, shape); } // 也可以使用 lambda 直接访问 std::cout \n使用 lambda 直接访问 area 和 perimeter:\n; for (const auto shape : shapes) { std::visit([](const auto s) { std::cout std::fixed std::setprecision(2) Area: s.area() , Perimeter: s.perimeter() \n; }, shape); } // 静态多态单独处理示例 std::cout \n静态多态单独处理:\n; Circle circle(5.0); Rectangle rectangle(4.0, 6.0); Triangle triangle(3.0, 4.0, 5.0); circle.printInfo(); rectangle.printInfo(); triangle.printInfo(); return 0; }以下是带基类虚函数用途二C 17#include iostream #include vector #include cmath #include variant #include memory #include iomanip // CRTP 基类模板 template typename Derived class Shape { public: double area() const { return static_castconst Derived*(this)-calculateArea(); } double perimeter() const { return static_castconst Derived*(this)-calculatePerimeter(); } void printInfo() const { std::cout std::fixed std::setprecision(2) Area: area() , Perimeter: perimeter() \n; } }; // 圆形 class Circle : public ShapeCircle { double radius; public: Circle(double r) : radius(r) {} double calculateArea() const { return M_PI * radius * radius; } double calculatePerimeter() const { return 2 * M_PI * radius; } }; // 矩形 class Rectangle : public ShapeRectangle { double width, height; public: Rectangle(double w, double h) : width(w), height(h) {} double calculateArea() const { return width * height; } double calculatePerimeter() const { return 2 * (width height); } }; // 三角形 class Triangle : public ShapeTriangle { double a, b, c; public: Triangle(double s1, double s2, double s3) : a(s1), b(s2), c(s3) {} double calculateArea() const { double s (a b c) / 2; return sqrt(s * (s - a) * (s - b) * (s - c)); } double calculatePerimeter() const { return a b c; } }; // 使用 std::variant 存储不同类型的形状 using ShapeVariant std::variantCircle, Rectangle, Triangle; // 访问者类用于调用 variant 中的对象的成员函数 class ShapeVisitor { public: void operator()(const Circle c) const { std::cout Circle: ; c.printInfo(); } void operator()(const Rectangle r) const { std::cout Rectangle: ; r.printInfo(); } void operator()(const Triangle t) const { std::cout Triangle: ; t.printInfo(); } }; int main() { // 创建不同类型的图形对象 Circle circle(5.0); Rectangle rectangle(4.0, 6.0); Triangle triangle(3.0, 4.0, 5.0); std::cout 单独处理每个形状:\n; circle.printInfo(); rectangle.printInfo(); triangle.printInfo(); std::cout \n使用 std::variant 统一处理:\n; // 创建 variant 的 vector std::vectorShapeVariant shapes; shapes.push_back(circle); shapes.push_back(rectangle); shapes.push_back(triangle); ShapeVisitor visitor; for (const auto shape : shapes) { std::visit(visitor, shape); } std::cout \n使用 lambda 表达式处理 variant:\n; for (const auto shape : shapes) { std::visit([](const auto s) { using T std::decay_tdecltype(s); if constexpr (std::is_same_vT, Circle) { std::cout Circle: ; } else if constexpr (std::is_same_vT, Rectangle) { std::cout Rectangle: ; } else if constexpr (std::is_same_vT, Triangle) { std::cout Triangle: ; } s.printInfo(); }, shape); } return 0; }C 11#include iostream #include vector #include cmath #include memory #include iomanip // 非模板基类用于类型擦除 class IShape { public: virtual double area() const 0; virtual double perimeter() const 0; virtual void printInfo() const 0; virtual ~IShape() default; }; // CRTP 基类模板 template typename Derived class Shape : public IShape { public: double area() const override { return static_castconst Derived*(this)-calculateArea(); } double perimeter() const override { return static_castconst Derived*(this)-calculatePerimeter(); } void printInfo() const override { std::cout std::fixed std::setprecision(2) Area: area() , Perimeter: perimeter() \n; } }; // 圆形 class Circle : public ShapeCircle { double radius; public: Circle(double r) : radius(r) {} double calculateArea() const { return M_PI * radius * radius; } double calculatePerimeter() const { return 2 * M_PI * radius; } }; // 矩形 class Rectangle : public ShapeRectangle { double width, height; public: Rectangle(double w, double h) : width(w), height(h) {} double calculateArea() const { return width * height; } double calculatePerimeter() const { return 2 * (width height); } }; // 三角形 class Triangle : public ShapeTriangle { double a, b, c; public: Triangle(double s1, double s2, double s3) : a(s1), b(s2), c(s3) {} double calculateArea() const { double s (a b c) / 2; return sqrt(s * (s - a) * (s - b) * (s - c)); } double calculatePerimeter() const { return a b c; } }; int main() { // 创建不同类型的图形对象 std::cout 使用基类指针统一处理:\n; // 使用基类指针的 vector std::vectorstd::unique_ptrIShape shapes; shapes.push_back(std::make_uniqueCircle(5.0)); shapes.push_back(std::make_uniqueRectangle(4.0, 6.0)); shapes.push_back(std::make_uniqueTriangle(3.0, 4.0, 5.0)); for (const auto shape : shapes) { shape-printInfo(); } // 单独处理每个形状静态多态 std::cout \n使用静态多态单独处理:\n; Circle circle(5.0); Rectangle rectangle(4.0, 6.0); Triangle triangle(3.0, 4.0, 5.0); circle.printInfo(); rectangle.printInfo(); triangle.printInfo(); return 0; }