一、RTTI
Run-time type information (RTTI) is a mechanism that allows the type of an object to be determined during program execution.
There are three main C++ language elements to run-time type information:
-
The dynamic_cast operator.
Used for conversion of polymorphic types.
-
The typeid operator.
Used for identifying the exact type of an object.
-
The type_info class.
Used to hold the type information returned by thetypeid operator.
class type_info {
public:virtual ~type_info();
bool operator==(const type_info& rhs) const;
bool operator!=(const type_info& rhs) const;
int before(const type_info& rhs) const;
const char* name() const;
const char* raw_name() const;private:
void *_m_data;
char _m_d_name[1];
type_info(const type_info& rhs);
type_info& operator=(const type_info& rhs);
static const char _Name_base(const type_info *,__type_info_node* __ptype_info_node);};
The result of typeid is a const type_info&. The value is a reference to a type_info object that represents either thetype-id or the type of theexpression, depending on which form oftypeid is used.
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72#include <iostream>
using
namespace std;class Shape
{
public:
virtual
void Draw() =
;
virtual ~Shape() {}
};class Circle :
public Shape
{
public:
void Draw()
{
cout <<
"Circle Draw ..." << endl;
}
};class Square :
public Shape
{
public:
void Draw()
{
cout <<
"Square Draw ..." << endl;
}
};int main(
void)
{
Shape *p;
Circle c;p = &c;
p->Draw();//使用dynamic_cast 的条件
//1、开启运行时类型信息；2、应用在具有多态关系的继承体系上；
if (
dynamic_cast<Circle *>(p))
{
cout <<
"p is point to a Circle object" << endl;
Circle *cp =
dynamic_cast<Circle *>(p);
// 安全向下转型
cp->Draw();
//效率没有 p->Draw(); 高
}
else
if (
dynamic_cast<Square *>(p))
{
cout <<
"p is point to a Square object" << endl;
}
else
{
cout <<
"p is point to a Other object" << endl;
}cout <<
typeid(*p).name() << endl;
cout <<
typeid(Circle).name() << endl;
if (
typeid(Circle).name() ==
typeid(*p).name())
{
cout <<
"p is point to a Circle object" << endl;
((Circle *)p)->Draw();
}
else
if (
typeid(Square).name() ==
typeid(*p).name())
{
cout <<
"p is point to a Circle object" << endl;
((Square *)p)->Draw();
}
else
{
cout <<
"p is point to a Other object" << endl;
}return
;
}
如上所述，dynamic_cast 和 typeid 操作符 都可以实现运行时类型识别。其中使用dynamic_cast 时需要开启运行时类型信息，在项目-》属性-》C/C++-》语言-》启用运行时类型信息。在使用typeid时需要注意的是返回的是type_info 对象的引用，且type_info 类的拷贝构造函数和赋值运算符都声明为私有，故不能这样写： type_info tf = typeid(Circle);
二、类与类之间的关系
Unified Modeling Language (UML)又称统一建模语言或标准建模语言,是始于1997年一个OMG标准，它是一个支持模型化和软件系统开发的图形化语言。
1、继承（泛化）Generalization
Manager 继承自Employee.
2、关联 Association，单向关联 DirectedAssociation
Order 作为Customer 的成员，如vector<Order> orders ;
3、聚合 Aggregation
class B
class A
{
public:
B* b_;
};
当A释放时，不负责B的释放，也许B是被共享的。
4、组合 Composition
当Company 释放时要负责Department 的释放，Department 不是共享的。
5、依赖 Dependency
类A依赖于B:
从语义上来上是A use B，偶然的，临时的
B作为A的成员函数参数
B作为A的成员函数的局部变量
A的成员函数调用B的静态方法比较5种关系：
继承体现的是类与类之间的纵向关系，其他4种体现的是类与类之间的横向关系。
关联强弱依赖<关联<聚合<组合
继承(A is B)
关联、聚合、组合(A has B)
依赖(A use B)
参考：
C++ primer 第四版
Effective C++ 3rd
C++编程规范