面向对象编程，使用静态函数计算对象

Question

我想用一个静态函数来显示类的对象和对象的数量。我输入了这段代码，但它不起作用。它给出了一个错误Too many types indeclaration" and "undefined symbol getCount。谁能帮我？这段代码的实际错误在哪里？

#include<iostream>
#include<string>

class Bag {
private:
    static int objectCount;
    int Weight;
    std::string Brand;
    std::string Type;
    std::string Material;
    std::string Colour;
public:
    Bag(int W, std::string B, std::string T, std::string M, std::string C) {
        Weight = W;
        Brand = B;
        Type = T;
        Material = M;
        Colour = C;
        objectCount++;
    }

    void print() {
        std::cout << "\n";
        std::cout << "Bag: \n\n";
        std::cout << "Weight:\t\t" << Weight   << "kg" << '\n';
        std::cout << "Brand:\t\t"  << Brand    << '\n' << "Type:\t\t"   << Type   << '\n';
        std::cout << "Material:\t" << Material << '\n' << "colour:\t\t" << Colour << std::endl;
    }

    static int getCount() {
        return objectCount;
    }
};

int Bag::objectCount = 0;

int main() {
    Bag bag_1(2, "Slazanger", "Atheletic Bag", "Polyethylene", "Brown");
    bag_1.print();
    std::cout << "object count " << Bag::getCount() << '\n';

    Bag bag_2(4, "Samsonite", "Travel Bag", "Synthetic Fibre", "Gray");
    bag_2.print();
    std::cout << "object count " << Bag::getCount() << '\n';

    Bag bag_3(5, "Herschel", "Duffel bag", "Leather", "Black");
    bag_3.print();
    std::cout << "object count " << Bag::getCount() << '\n';

    Bag bag_4(3, "Kewin Woods", "Hand Bag", "Fibre", "Blue");
    bag_4.print();
    std::cout << "object count " << Bag::getCount() << std::endl;

    while(!std::cin.get());
    return 0;
}

Answer 1

您的范围不正确，getCount 是静态范围内的翻译 单位，而不是班级。因此它没有可用的名为objectCount 的符号。

要修复它，只需将方法放在类中即可。

class Bag {
private:
    static int objectCount;
    int Weight;
    string Brand,Type,Material,Colour;
public:
    Bag(int W ,string B ,string T,string M,string C)
    {
        Weight=W;
        Brand=B;
        Type=T;
        Material=M;
        Colour=C;

        objectCount++;
    }

    void print()
    {
        cout<<"\n";
        cout<<"Bag: \n\n";
        cout<<"Weight:\t\t"<<Weight<<"kg"<<endl;
        cout<<"Brand:\t\t"<<Brand<<endl<<"Type:\t\t"<<Type<<endl;
        cout<<"Material:\t"<<Material<<endl<<"colour:\t\t"<<Colour<<endl;
    }

   static int getCount()
   {
       cout<< objectCount;
   }
};

此外，Borland 是一个非常古老的编译器，甚至仍然令人惊讶 听说它的名字，上一次发布是在 15 年前，所以你真的应该 考虑使用clang、gcc 或msvc 并将您的学习材料升级到 不那么古老的东西。在实践方面已经有了很大的发展， 标准和编译器一致性。

例如，C++ 头文件没有扩展名，以及其他类似的小东西。

Answer 2

这是您的代码的工作版本：

#include <iostream>
#include <cstring>

using namespace std;

class Bag {
private:
  static int objectCount;
  int Weight;
  string Brand, Type, Material, Colour;

public:
  Bag(int W, string B, string T, string M, string C) //constructor
  {
    Weight = W;
    Brand = B;
    Type = T;
    Material = M;
    Colour = C;

    objectCount++;
  }
  void print() {
    cout << "\n";
    cout << "Bag: \n\n";
    cout << "Weight:\t\t" << Weight << "kg" << endl;
    cout << "Brand:\t\t" << Brand << endl << "Type:\t\t" << Type << endl;
    cout << "Material:\t" << Material << endl << "colour:\t\t" << Colour
         << endl;
  }
  static int getCount() //static function to count objects
  {
    cout << objectCount;
  };
};


int Bag::objectCount = 0;
int main() {

  Bag bag_1(2, "Slazanger", "Atheletic Bag", "Polyethylene", "Brown");

  Bag bag_2(4, "Samsonite", "Travel Bag", "Synthetic Fibre", "Gray");
  Bag bag_3(5, "Herschel", "Duffel bag", "Leather", "Black");
  Bag bag_4(3, "Kewin Woods", "Hand Bag", "Fibre", "Blue");
  bag_1.print();
  cout << "object count" << Bag::getCount();
  bag_2.print();
  cout << "object count" << Bag::getCount();

  bag_3.print();
  cout << "object count" << Bag::getCount();

  bag_4.print();
  cout << "object count" << Bag::getCount();
}

您发布的版本有几个错误：

• 在 C++ 中，包含文件时不需要 .h
• 您使用的cout 没有std:: 限定符或将using namespace std; 添加到您的源。另外，请阅读this。
• 您的静态函数未在您的类定义中声明/定义
• 应该是int main 而不是void main

最后一点：我删除了您的#include <conio.h>，它可能应该是#include <conio> 和getch，因为我是在Linux 机器上编译的。如果需要，请随时将它们重新添加。