用主文件中的类初始化函数的方法是什么？

Question

这个程序是一个 c++ 项目，使用谷仓和动物的类来创建一个动物谷仓。这些动物通过它们的名字、类型和重量来识别。在特定时间，动物会进食并增加体重。用户可以选择要经过多少天。大部分代码都已经写好了，现在是让 main 使用类函数的问题了。当我尝试在 main 中执行功能时，我收到错误代码“main.cpp:117:28: error: 'class Animal' has no member named 'display'” 相对于以下行：cout 显示（） 这是代码。

// C++ program to create classes for Barn of Animals
#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <vector>
using namespace std;

int main()
{
    //I need to run the program so a unit of time passes
    //When the time runs, the time will be compared to
    //the animals feeding time.  When that feed time passes, 
    //The animal gains weight and the new weight is shown.
    int choice;

    cout << "1) Simulate Days" << endl;
    cout << "2) Display Animals" << endl;
    cout << "3) Exit" << endl;

    cout << "Choose an option: \n";
    cout << "Enter 1, 2 or 3: ";
    cin >> choice;
    switch (choice)
    {
        case 1:
            cout << "Choice 1";
            break;  //Here we will run feedAnimal
        case 2:
            cout << "Choice 2";
            break;  //Here we will display all the animals
        case 3:
            cout << "Choice 3";
            break;  //Here we will exit the program
        default:
            cout << "Not 1, 2 or 3";
            break;
    }
}

// base Animal class
class Animal
{
    private:
        // data members
        string type;
    string name;
    int weight;
    public:
        // constructor to initialize the members to specified values
        Animal(string type, string name, int weight): type(type), name(name), weight(weight) {}

    // getters
    string getType()
    {
        return type;
    }

    string getName()
    {
        return name;
    }

    int getWeight()
    {
        return weight;
    }

    // setter for weight
    void setWeight(int weight)
    {
        this->weight = weight;
    }
};

// derived class Horse
class Horse: public Animal
{
    public: Horse(string name, int weight): Animal("horse", name, weight) {}
};

// derived class Cow
class Cow: public Animal
{
    public: Cow(string name, int weight): Animal("cow", name, weight) {}
};

// derived class Chicken
class Chicken: public Animal
{
    public: Chicken(string name, int weight): Animal("chicken", name, weight) {}
};

class Barn
{
    private:
        vector<Animal*> barn;

    public:
        Barn();
    void feedAnimal();

};

Barn::Barn()
{
    srand(time(0)); // this will be srand not rand
    Animal * a;

    for (int i = 0; i < 5; i++)
    {
        a = new Horse("Artax" + to_string(i + 1), rand() % 200 + 1820); // end with semicolon not colon
        barn.push_back(a);

        a = new Cow("Fafnir" + to_string(i + 1), rand() % 250 + 1200);  // convert (i+1) to string not (i+)
        barn.push_back(a);

        a = new Chicken("David" + to_string(i + 1), rand() % 2 + 15);
        barn.push_back(a);

        for (int i = 0; i < barn.size(); i++)
        {
            cout << barn[i]->display() << " " << " ";   //This Displays all the animals

        }
    }

    void Barn::feedAnimal()
    {
        int days;   // = 0;
        cout << "how many days:";
        cin >> days;

        for (int day = 0; day < days; day++)
        {
            for (int i = 1; i <= 12; i++)
            {
                string feed = to_string(i) + ":00"; // define the type for feed

                cout << "The Time is " << feed << "\n";

                if (i == 3) // time is 3:00, feed the chickens
                {
                    // loop over the vector of Animals to feed the Chicken
                    for (size_t i = 0; i < barn.size(); i++)
                    {
                        if (barn[i]->getType() == "chicken")    // this animal is chicken
                            barn[i]->setWeight(barn[i]->getWeight() + 1);   // add 1 pound to its weight
                        cout << name << " " << type << " now weighs " << getweight() << " lbs";
                    }
                }
                else if (i == 5)    // time is 5:00, feed the horses
                {
                    // loop over the vector of Animals to feed the Horse
                    for (size_t i = 0; i < barn.size(); i++)
                    {
                        if (barn[i]->getType() == "horse")  // this animal is horse

                            barn[i]->setWeight(barn[i]->getWeight() + 5);   // add 5 pound to its weight
                        cout << name << " " << type << " now weighs " << getweight() << " lbs";
                    }
                }
                else if (i == 7)    // time is 7:00, feed the cows
                {
                    // loop over the vector of Animals to feed the Cow
                    for (size_t i = 0; i < barn.size(); i++)
                    {
                        if (barn[i]->getType() == "cow")    // this animal is cow
                            barn[i]->setWeight(barn[i]->getWeight() + 5);   // add 5 pound to its weight
                        cout << name << " " << type << " now weighs " << getweight() << " lbs";
                    }
                }
            }
        }
    }
}

Answer 1

好的，这就是我的工作方式。感谢大家的帮助，真的帮了我大忙。

//Fixed Practice code

#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <vector>

using namespace std;

// base Animal class
class Animal {
private:
    // data members
    string type;
    string name;
    int weight;
public:
    // constructor to initialize the members to specified values
    //Animal(string type, string name, int weight) : type(type), name(name), weight(weight)
    Animal(string type, string name, int weight) {
        //Added code to called the setters
        setWeight(weight);
        setName(name);
        setType(type);
    }

    // getters
    string getType() { return type; }
    string getName() { return name; }
    int getWeight() { return weight; }

    //Added setter for type
    void setType(string type) { this->type = type; }
    //Added setter for name
    void setName(string name) { this->name = name; }
    // setter for weight
    void setWeight(int weight) { this->weight = weight; }

    //Added the display method in the Animal class to display the animal details
    string display() {
        string printLine = "";
        printLine = "\nAnimal Type: " + this->getType() + ", Animal Name: " + this->getName() + ", Animal Weight: " + to_string(this->getWeight());
        return printLine;
    }
};

// derived class Horse
class Horse : public Animal {
public:
    Horse(string name, int weight) : Animal("horse", name, weight)
    {}
};

// derived class Cow
class Cow : public Animal {
public:
    Cow(string name, int weight) : Animal("cow", name, weight)
    {}
};

// derived class Chicken
class Chicken : public Animal {
public:
    Chicken(string name, int weight) : Animal("chicken", name, weight)
    {}
};

class Barn {
private:
    vector<Animal*> barn;

public:
    Barn();
    void feedAnimal();
    void display();

};

Barn::Barn() {
    srand(time(0)); // this will be srand not rand
    Animal* a;
    for (int i = 0; i < 5;i++) {
        a = new Horse("Artax" + to_string(i + 1), rand() % 200 + 1820); // end with semicolon not colon
        barn.push_back(a);

        a = new Cow("Fafnir" + to_string(i + 1), rand() % 250 + 1200); // convert (i+1) to string not (i+)
        barn.push_back(a);

        a = new Chicken("David" + to_string(i + 1), rand() % 2 + 15);
        barn.push_back(a);
    }

}

//Added the display code here, moved the code from inside the Barn constructor
void Barn::display() {
    for (int i = 0; i < barn.size(); i++) {
        cout << barn[i]->display() << " " << " "; //This Displays all the animals
    }
}

void Barn::feedAnimal() {
    int days;// = 0;
    string feed;
    cout << "\nhow many days:";
    cin >> days;
    //Added the code here - Sort of modifications
    //We are looping the vector once, check the time and animal increase the weight, the prior code was looping the vector multiple times for a day and time
    for (int day = 0; day < days;day++) {
        for (int feedtime = 1; feedtime <= 12; feedtime++) {
            feed = to_string(feedtime) + ":00"; // define the type for feed
            cout << "\nThe Time is " << feed << "\n";
            for (int barnNum = 0; barnNum < barn.size();barnNum++) {
                if ((feedtime == 3) && (barn[barnNum]->getType() == "chicken")) {
                    barn[barnNum]->setWeight(barn[barnNum]->getWeight() + 1); // add 1 pound to its weight
                    cout << "\n" << barn[barnNum]->getName() << " " << barn[barnNum]->getType() << " now weighs " << barn[barnNum]->getWeight() << " lbs";
                }

                if ((feedtime == 5) && (barn[barnNum]->getType() == "horse")) {
                    barn[barnNum]->setWeight(barn[barnNum]->getWeight() + 5); // add 5 pound to its weight
                    cout << "\n" << barn[barnNum]->getName() << " " << barn[barnNum]->getType() << " now weighs " << barn[barnNum]->getWeight() << " lbs";
                }

                if ((feedtime == 7) && (barn[barnNum]->getType() == "cow")) {
                    barn[barnNum]->setWeight(barn[barnNum]->getWeight() + 5); // add 5 pound to its weight
                    cout << "\n" << barn[barnNum]->getName() << " " << barn[barnNum]->getType() << " now weighs " << barn[barnNum]->getWeight() << " lbs";
                }
            }
        }
    }
}

int main()
{
    //I need to run the program so a unit of time passes
    //When the time runs, the time will be compared to
    //the animals feeding time. When that feed time passes,
    //The animal gains weight and the new weight is shown.
    int choice;

    cout << "1) Simulate Days" << endl;
    cout << "2) Display Animals" << endl;
    cout << "3) Exit" << endl;
    //Added code to create a Barn object
    Barn myBarn;
    cout << "Choose an option: \n";
    cout << "Enter 1, 2 or 3: ";
    cin >> choice;
    switch (choice)
    {
    case 1:
        cout << "\nChoice 1"; //Here we will run feedAnimal
        //Call the feedAnimal() method
        myBarn.feedAnimal();
        break;
    case 2:
        cout << "\nChoice 2";
        //Call the display() method
        myBarn.display();
        break;//Here we will display all the animals
    case 3:
        cout << "\nChoice 3"; break;//Here we will exit the program
    default:
        cout << "\nNot 1, 2 or 3"; break;
    }
}

Answer 2

在Animal 类中，您只需实现返回字符串的display() 方法，更改后一切正常：

std::string display() const {
    std::stringstream ss;
    ss << "type: " << type << ", name: " << name
        << ", weights: " << weight << std::endl;
    return ss.str();
}

下面的完整更正代码。还必须修正一些错别字以使代码可编译：

Try it online!

// C++ program to create classes for Barn of Animals
#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <vector>
#include <sstream>

using namespace std;

int main()
{
    //I need to run the program so a unit of time passes
    //When the time runs, the time will be compared to
    //the animals feeding time.  When that feed time passes, 
    //The animal gains weight and the new weight is shown.
    int choice;

    cout << "1) Simulate Days" << endl;
    cout << "2) Display Animals" << endl;
    cout << "3) Exit" << endl;

    cout << "Choose an option: \n";
    cout << "Enter 1, 2 or 3: ";
    cin >> choice;
    switch (choice)
    {
        case 1:
            cout << "Choice 1";
            break;  //Here we will run feedAnimal
        case 2:
            cout << "Choice 2";
            break;  //Here we will display all the animals
        case 3:
            cout << "Choice 3";
            break;  //Here we will exit the program
        default:
            cout << "Not 1, 2 or 3";
            break;
    }
}

// base Animal class
class Animal {
private:
    // data members
    string type;
    string name;
    int weight;

public:
    // constructor to initialize the members to specified values
    Animal(string type, string name, int weight): type(type), name(name), weight(weight) {}

    // getters
    string getType()
    {
        return type;
    }

    string getName()
    {
        return name;
    }

    int getWeight()
    {
        return weight;
    }

    // setter for weight
    void setWeight(int weight)
    {
        this->weight = weight;
    }

    std::string display() const {
        std::stringstream ss;
        ss << "type: " << type << ", name: " << name
            << ", weights: " << weight << std::endl;
        return ss.str();
    }
};

// derived class Horse
class Horse: public Animal
{
    public: Horse(string name, int weight): Animal("horse", name, weight) {}
};

// derived class Cow
class Cow: public Animal
{
    public: Cow(string name, int weight): Animal("cow", name, weight) {}
};

// derived class Chicken
class Chicken: public Animal
{
    public: Chicken(string name, int weight): Animal("chicken", name, weight) {}
};

class Barn
{
private:
    vector<Animal*> barn;

public:
    Barn();
    void feedAnimal();
};

Barn::Barn() {
    srand(time(0)); // this will be srand not rand
    Animal * a;

    for (int i = 0; i < 5; i++)
    {
        a = new Horse("Artax" + to_string(i + 1), rand() % 200 + 1820); // end with semicolon not colon
        barn.push_back(a);

        a = new Cow("Fafnir" + to_string(i + 1), rand() % 250 + 1200);  // convert (i+1) to string not (i+)
        barn.push_back(a);

        a = new Chicken("David" + to_string(i + 1), rand() % 2 + 15);
        barn.push_back(a);

        for (int i = 0; i < barn.size(); i++)
        {
            cout << barn[i]->display() << " " << " ";   //This Displays all the animals
        }
    }
}

void Barn::feedAnimal()
{
    int days;   // = 0;
    cout << "how many days:";
    cin >> days;

    for (int day = 0; day < days; day++)
    {
        for (int i = 1; i <= 12; i++)
        {
            string feed = to_string(i) + ":00"; // define the type for feed

            cout << "The Time is " << feed << "\n";

            if (i == 3) // time is 3:00, feed the chickens
            {
                // loop over the vector of Animals to feed the Chicken
                for (size_t i = 0; i < barn.size(); i++)
                {
                    if (barn[i]->getType() == "chicken")    // this animal is chicken
                        barn[i]->setWeight(barn[i]->getWeight() + 1);   // add 1 pound to its weight
                    //cout << name << " " << type << " now weighs " << getWeight() << " lbs";
                    cout << barn[i]->display();
                }
            }
            else if (i == 5)    // time is 5:00, feed the horses
            {
                // loop over the vector of Animals to feed the Horse
                for (size_t i = 0; i < barn.size(); i++)
                {
                    if (barn[i]->getType() == "horse")  // this animal is horse

                        barn[i]->setWeight(barn[i]->getWeight() + 5);   // add 5 pound to its weight
                    //cout << name << " " << type << " now weighs " << getWeight() << " lbs";
                    cout << barn[i]->display();
                }
            }
            else if (i == 7)    // time is 7:00, feed the cows
            {
                // loop over the vector of Animals to feed the Cow
                for (size_t i = 0; i < barn.size(); i++)
                {
                    if (barn[i]->getType() == "cow")    // this animal is cow
                        barn[i]->setWeight(barn[i]->getWeight() + 5);   // add 5 pound to its weight
                    //cout << name << " " << type << " now weighs " << getWeight() << " lbs";
                    cout << barn[i]->display();
                }
            }
        }
    }
}

Answer 3

不是编写一个完全独立的函数，而是操作符

#include <iostream>

class MyClass {
    int i = 0;
public: 
    MyClass() : i(4) { }
    friend std::ostream& operator<<(std::ostream& out, MyClass obj) {
        out << obj.i;
        return out;
    }
};

int main() {
    MyClass myClass;
    std::cout << myClass;
    return 0;
}