C++虚函数解析问题

Question

程序在此函数调用解析中抛出错误：

for(vector<Catalog*>::iterator i=m_subDeptList.begin(); i!=m_subDeptList.end();  ++i)
         (*i)->displayDiscription();

错误：

test.cpp: In member function ‘void Department::displayDiscription()’:
test.cpp:73:14: error: ‘class Catalog’ has no member named ‘displayDiscription’
    (*i)->displayDiscription();

但以下呼叫解决方案没有问题：

for(vector<Product*>::iterator i=m_products.begin(); i!=m_products.end();  ++i)
        (*i)->displayDiscription();
for(vector<Catalog*>::iterator i=m_subDeptList.begin() ; i!=m_subDeptList.end();  ++i)
        (*i)->addDiscount(discount);
for(vector<Product*>::iterator  i=m_products.begin(); i!=m_products.end();  ++i)
        (*i)->addDiscount(discount);

有人能解释一下吗？

#include <cstdlib>
#include <iostream>
#include <vector>

using namespace std;

class Catalog
{
    string m_name;
public:
    Catalog(const string &name):m_name(name){}
    //virtual ~Catalog(){}
    const string& getName()
    {
        return m_name;
    }

    virtual bool addDiscount(unsigned int discount)=0;
    virtual void displayDescription()=0;      
};
class Product:public Catalog
{
    unsigned short m_discount; // discount in %
    long double m_price;
public:
    Product(const string& productName, const long double &price):Catalog(productName),m_price(price){}
    void displayDiscription()
    {
        cout<<getName()<<"price: "<<getPrice()<<endl;
    }    
    bool addDiscount(const unsigned int discount)
    {
        if( discount > 100 || discount < 0)
            return false;
        m_discount+=discount;
        return true;
    }
    long double getPrice()
    {
        return m_price;
    }

};
class Department:public Catalog
{
    vector<Product*> m_products;
    vector<Catalog*> m_subDeptList;
    unsigned int discountApplied;
public:
    Department(const string &name):Catalog(name){}

    bool addDiscount(unsigned int discount) // add discount to all products in this dept/subDept
    {
        if( discount > 100 || discount < 0)
            return false;

        for(vector<Catalog*>::iterator i=m_subDeptList.begin() ; i!=m_subDeptList.end();  ++i)
            (*i)->addDiscount(discount);
        for(vector<Product*>::iterator  i=m_products.begin(); i!=m_products.end();  ++i)
            (*i)->addDiscount(discount);
        discountApplied+=discount;
        return true;
    }    

    void displayDiscription()
    {

        cout<<getName()<<endl;

        if(!m_subDeptList.empty() )
        for(vector<Catalog*>::iterator i=m_subDeptList.begin(); i!=m_subDeptList.end();  ++i)
             (*i)->displayDiscription();

        if(!m_products.empty() )
            for(vector<Product*>::iterator i=m_products.begin(); i!=m_products.end();  ++i)
            (*i)->displayDiscription();

        return;

    }  
/*
    void addProduct(Product* pProduct)
    {
        m_products.push_back(pProduct);

    }
    void addDepartment(Catalog* pDepartment)
    {
        m_subDeptList.push_back(pDepartment);

    }
*/
};

int main(int argc, char** argv) {
/*    
    Department megaStoreCatalog("catalog");
    Department stationary("Stationary");
    Product pen("pen", 5);
    stationary.addProduct(&pen);
    Department stationaryLiquid("Stationary-Liquid");
    Product ink("Bril",30);
    stationaryLiquid.addProduct(&ink);
    megaStoreCatalog.addDepartment(&stationary);
    stationary.addDepartment(&stationaryLiquid);

    megaStoreCatalog.addDiscount(10);

  */  
    return 0;
}

Answer 1

您不能只在 addDiscount 中添加 const。它改变了函数签名。

您应该使用 C++11 override keyword。

Answer 2

无法解析，因为在该纯虚函数声明的基础 class 签名中找不到您的两个派生 classes 方法。您的问题不是实现问题，而是拼写错误。

查看您在 Base 和 Derived classes 中的拼写；您将一个拼写为 discription，将另一个拼写为 description。此外，您还拥有一种带有 const 的纯虚方法，但在基础 class 中未以这种方式定义。另一件事是您的构造函数只有 1 个参数，因此您应该在其名称前使用 explicit 关键字声明该构造函数。您不应该在基类中使用默认构造函数，即使它是空的或什么都不做并将其声明为虚拟的。

在你的基地Class

virtual void displayDescription()=0;

在你的派生 Classes

void displayDiscription()
{
    cout<<getName()<<"price: "<<getPrice()<<endl;
}

&

void displayDiscription()
{

    cout<<getName()<<endl;

    if(!m_subDeptList.empty() )
    for(vector<Catalog*>::iterator i=m_subDeptList.begin(); i!=m_subDeptList.end();  ++i)
         (*i)->displayDiscription();

    if(!m_products.empty() )
        for(vector<Product*>::iterator i=m_products.begin(); i!=m_products.end();  ++i)
        (*i)->displayDiscription();

    return;

}

C++虚函数解析问题

C++ virtual function resolution issue

c++

virtual

function