问题：类b公有继承类a，类a有虚函数fun，类b覆盖了虚函数fun，有一个std::vector<a>，添加a的对象a，和b的对象b，到这个容器里，然后从vector里取出来，使用对象a.fun()，和对象b.fun()，会发生什么？

发现对象b.fun()的调用，实际调用的是父类a的fun()方法。也就是子类部分被切掉了。

如何解决呢，用std::vector<a*>或者std::vector<std::shared_ptr<a>> ，但推荐用智能指针。

quote3.h

#ifndef __quote3_h__ #define __quote3_h__  #include <iostream> #include <memory>  class quote{  public:   quote() = default;   quote(const std::string& book, double pri)     :bookno(book), price(pri){}   std::string isbn() const{return bookno;}   virtual double net_price(std::size_t n)const{     return n * price;   }   virtual void debug()const{     std::cout << bookno << " " << price << std::endl;   }   virtual ~quote() = default;  private:   std::string bookno;  protected:   double price = 0.0; };  class disc_quote : public quote{  public:   disc_quote() = default;   disc_quote(const std::string& book, double price,          std::size_t qyn, double disc):quote(book, price),     quantity(qyn), discount(disc){}      double net_price(std::size_t) const override = 0;  protected:   std::size_t quantity = 0;//折扣适用的数量   double discount = 0.0;   //折扣率 };  class bulk_quote : public disc_quote{  public:      bulk_quote() = default;      bulk_quote(const std::string& book, double price,   std::size_t qyn, double disc)   :disc_quote(book, price, qyn, disc){}      double net_price(std::size_t) const override; };  class min_quote : public disc_quote{  public:    min_quote() = default;   min_quote(const std::string& book, double price,        std::size_t qyn, double disc)    :disc_quote(book, price, qyn, disc){}      double net_price(std::size_t) const override; };  #endif 

quote3.cpp

#include "quote3.h"  double bulk_quote::net_price(std::size_t cnt) const{   if(cnt >= quantity){     return cnt * (1 - discount) * price;   }   else{     return cnt * price;   } }   double min_quote::net_price(std::size_t cnt) const{   if(cnt < quantity){     return cnt * (1 - discount) * price;   }   else{     return cnt * price;   } }  

main.cpp

#include "quote3.h" #include <vector>  double print_total(std::ostream& os,            const quote& item, size_t n){   double ret = item.net_price(n);   os << "isbn: " << item.isbn()      << " # sold: " << n << " total due: " << ret << std::endl;   return ret;  }  int main(){    std::vector<quote> qv;   for(unsigned i = 0; i != 10; ++i){     qv.push_back(bulk_quote("01", 100, 10, 0.1));   }   double total = 0;   for(const auto s : qv){     total += s.net_price(20);   }   std::cout << total << std::endl;    std::cout << "-------------------------" << std::endl;    std::vector<std::shared_ptr<quote>> sv;   for(unsigned i = 0; i != 10; ++i){     sv.push_back(std::make_shared<bulk_quote>("01", 100, 10, 0.1));   }   double total1 = 0;   for(const auto s : sv){     total1 += s->net_price(20);   }   std::cout << total1 << std::endl;    } 

执行结果：

20000 ------------------------- 18000

std::vecto<quote>的执行结果为：20000；std::vector<std::shared_ptr<quote>>部分的执行结果：18000。所以在容器里放智能指针，可以解决上面的问题。