RTTI、dynamic_cast、typeid、類與類之間的關係uml

時間 2020-07-14

標籤 rtti dynamic cast typeid 之間關係 uml 简体版

原文原文鏈接

1、RTTInode

Run-time type information (RTTI) is a mechanism that allows the type of an object to be determined during program execution.
ios

There are three main C++ language elements to run-time type information:express

The dynamic_cast operator. 編程

Used for conversion of polymorphic types. 安全
The typeid operator. ide

Used for identifying the exact type of an object.函數

The type_info class. spa

Used to hold the type information returned by the typeid operator. orm

class type_info {
public:
對象

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 the type-id or the type of the expression, depending on which form of typeid is used.

爲了支持RTTI，爲每個多態類建立一個type_info 對象（靜態數據區），並把其地址保存到vtable中的固定位置（通常爲第一個位置）（取決於具體編譯器實現，標準並無規定）。

C++ Code

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#include <iostream>
using namespace std;

class Shape
{
public:
    virtual void Draw() = 0;
    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 的條件
    //一、開啓運行時類型信息；二、應用在具備多態關係的繼承體系上；
    if (dynamic_cast<Circle *>(p))
    {
        cout << "p is point to a Circle object" << endl;
        Circle *cp = dynamic_cast<Circle *>(p);     // 安全向下轉型
        cp->Draw(); //效率沒有 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 0;
}

如上所述，dynamic_cast 和 typeid 操做符均可以實現運行時類型識別。其中使用dynamic_cast 時須要開啓運行時類型信息，在項目-》屬性-》C/C++-》語言-》啓用運行時類型信息。在使用typeid時須要注意的是返回的是type_info 對象的引用，且type_info 類的拷貝構造函數和賦值運算符都聲明爲私有，故不能這樣寫： type_info tf = typeid(Circle);

2、類與類之間的關係

Unified Modeling Language (UML)又稱統一建模語言或標準建模語言,是始於1997年一個OMG標準，它是一個支持模型化和軟件系統開發的圖形化語言。

一、繼承（泛化）Generalization

Manager 繼承自Employee.

二、關聯 Association，單向關聯 DirectedAssociation

Order 做爲Customer 的成員，如vector<Order> orders ;

三、聚合 Aggregation

class B

class A

{