在下面的代码中，我试图创建一个函数“patient_count”，它是“horse”，“pig”和“dog”类的朋友。我可以让这个功能成为一个班级的朋友而不是所有的3个人。任何人都能告诉我我的错误是什么吗？
/*******************************************************\
* Veternarian Class Problem - I need a class for each *
* of 3 animals. Horse, Pig and Dogs *
\*******************************************************/
#include <cstdlib>
#include <iostream>
#include <string>
const int HORSE_KENNEL = 100; // Number of horses we can store
const int PIG_KENNEL = 100; // Number of Pigs we can store
const int DOG_KENNEL = 100; // Number of Dogs we can store
/*******************************************************\
* Class horse *
* *
* Member functions *
* horse_count -- Keeps track of the number of horses *
* add_horse -- Sends data into the object *
* next_horse -- returns data from the object *
\*******************************************************/
// Definition of the Class
class horse {
private:
int horse_count; // Variable to keep track of data
std::string horse_data[HORSE_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
horse( );
// A Function that accepts an argument but returns nothing
void add_horse(const std::string new_horse_data);
// This method returns the next Horse in the queue
std::string next_horse( );
friend int patient_count(horse);
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline horse::horse( )
{
for(int i = 0; i < HORSE_KENNEL; ++i){
horse_data[i] = "Empty Spot";
}
horse_count = 0; // Zero the data count
}
/*******************************************************\
* horse::add_horse -- Send data to Object *
\*******************************************************/
inline void horse::add_horse(const std::string new_horse_data)
{
horse_data[horse_count] = new_horse_data;
++horse_count;
}
/*******************************************************\
* horse::next_horse - get data from object *
\*******************************************************/
inline std::string horse::next_horse( )
{
// this is specifically implementing a queue
std::string current_horse = " ";
int target_horse = 0;
for(int i = 0;i < HORSE_KENNEL; ++i){
if(horse_data[i] != "Empty Spot"){
std::cout << "Horse Number " << i << " " << horse_data[i] << std::endl;
}
}
std::cout << "Select the horse you want: ";
std::cin >> target_horse;
return (horse_data[target_horse]);
}
/*******************************************************\
* Class Pig *
* *
* Member functions *
* pig_count -- Keeps track of the number of pigs *
* add_pig -- Sends data into the object *
* next_pig -- returns data from the object *
\*******************************************************/
// Definition of the Class
class pig {
private:
int pig_count; // Variable to keep track of data
std::string pig_data[PIG_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
pig( );
// A Function that accepts an argument but returns nothing
void add_pig(const std::string new_pig_data);
// This method returns the next pig in the queue
std::string next_pig( );
friend pig patient_count(pig);
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline pig::pig( )
{
for(int i = 0; i < PIG_KENNEL; ++i){
pig_data[i] = "Empty Spot";
}
pig_count = 0; // Zero the data count
}
/*******************************************************\
* pig::add_pig -- Send data to Object *
\*******************************************************/
inline void pig::add_pig(const std::string new_pig_data)
{
pig_data[pig_count] = new_pig_data;
++pig_count;
}
/*******************************************************\
* pig::next_pig - get data from object *
\*******************************************************/
inline std::string pig::next_pig( )
{
// this is specifically implementing a queue
std::string current_pig = " ";
int target_pig = 0;
for(int i = 0;i < PIG_KENNEL; ++i){
if(pig_data[i] != "Empty Spot"){
std::cout << "pig Number " << i << " " << pig_data[i] << std::endl;
}
}
std::cout << "Select the pig you want: ";
std::cin >> target_pig;
return (pig_data[target_pig]);
}
/*******************************************************\
* Class dog *
* *
* Member functions *
* dog_count -- Keeps track of the number of dogs *
* data_to_object -- Sends data into the object *
* data_from_object -- returns data from the object *
\*******************************************************/
// Definition of the Class
class dog {
private:
int dog_count; // Variable to keep track of data
std::string dog_data[DOG_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
dog( );
// A Function that accepts an argument but returns nothing
void add_dog(const std::string new_dog_data);
// This method returns the next dog in the queue
std::string next_dog( );
friend dog patient_count(dog);
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline dog::dog( )
{
for(int i = 0; i < DOG_KENNEL; ++i){
dog_data[i] = "Empty Spot";
}
dog_count = 0; // Zero the data count
}
/*******************************************************\
* dog::add_dog -- Send data to Object *
\*******************************************************/
inline void dog::add_dog(const std::string new_dog_data)
{
dog_data[dog_count] = new_dog_data;
++dog_count;
}
/*******************************************************\
* dog::next_dog - get data from object *
\*******************************************************/
inline std::string dog::next_dog( )
{
// this is specifically implementing a queue
std::string current_dog = " ";
int target_dog = 0;
for(int i = 0;i < DOG_KENNEL; ++i){
if(dog_data[i] != "Empty Spot"){
std::cout << "dog Number " << i << " " << dog_data[i] << std::endl;
}
}
std::cout << "Select the dog you want: ";
std::cin >> target_dog;
return (dog_data[target_dog]);
}
/**************************************************\
* This function is a friend of all the animal *
* classes and returns the total of all animals *
* PROBLEM ******* PROBLEM *********PROBLEM *********
* When I add the other 2 classes on the next line *
* The program stops working *
\**************************************************/
// int patient_count(horse target_horse) //works
int patient_count(horse target_horse, pig target_pig, dog target_dog) // Nova
{
// int all_animals = target_horse.horse_count; //Works
int all_animals = target_horse.horse_count + target_pig.pig_count + target_dog.dog_count; // Nova
return (all_animals);
}
/**************************************************\
* The Class is defined above, this section is a *
* Small testing harness to verify that the class *
* is doing what it was designed to do *
\**************************************************/
int main( )
{
int total_animals;
horse current_horse; // Create a instance
// Send 3 values to the object
current_horse.add_horse("Mr Ed, 10, Male");
current_horse.add_horse("Lightning, 4, Female");
current_horse.add_horse("Blitz, 7, Male");
// Call for the return of the 3 values
std::cout << "Selected Horse ->" << current_horse.next_horse( ) << '\n';
pig current_pig; // Create a instance
// Send 3 values to the object
current_pig.add_pig("Arnold, 4, Male");
current_pig.add_pig("Babe, 2, Female");
current_pig.add_pig("Killer, 7, Male");
// Call for the return of the 3 values
std::cout << "Selected Pig ->" << current_pig.next_pig( ) << '\n';
dog current_dog; // Create a instance
// Send 3 values to the object
current_dog.add_dog("Misty, 15, Female");
current_dog.add_dog("Tristian, 12, Male");
current_dog.add_dog("Tempest, 11, Female");
// Call for the return of the 3 values
std::cout << "Selected Dog ->" << current_dog.next_dog( ) << '\n';
// Now get the results from the friend function
// total_animals = patient_count(current_horse); // Works
total_animals = patient_count(current_horse, current_pig, current_dog); // Nova
std::cout << "Total Animals: " << total_animals << std::endl;
return (0);
}
答案 0 :(得分：5)
在为每个类声明它们时，需要使用适当的签名/声明来定义适当的友元函数patient_count。
现在你有一个patient_count函数定义了签名：
int patient_count(horse target_horse, pig target_pig, dog target_dog);
在各个类中声明的友元函数都带有签名：
dog patient_count(dog);
int patient_count(horse);
pig patient_count(pig);
您需要为每个签名定义功能。 您使用3个输入参数定义的函数几乎没用，因为它未被声明为您的任何类的朋友。
请注意，在C ++中，函数被重载（每个函数都有独立的存在）基于：
因此，这些功能中的每一个都是独立的，并且不相同，需要单独的定义。
答案 1 :(得分：2)
嗯......我认为有一个很多更容易处理这个问题：
class animal {
static int count;
animal() { ++count; }
~animal() { --count; }
};
class horse : public animal {
// horse stuff
};
class pig : public animal {
// pig stuff here
};
class dog : public animal {
// dog stuff here
};
int patient_count() { return animal::count; }
除此之外，你的代码似乎有一个相当基本的问题：它使一群动物的动物感到困惑（例如）。你有很多事情：
dog current_dog; // Create a instance
// Send 3 values to the object
current_dog.add_dog("Misty, 15, Female");
current_dog.add_dog("Tristian, 12, Male");
current_dog.add_dog("Tempest, 11, Female");
这没有任何意义。一只狗应该代表：一只狗。它有一个名字，一个年龄，一个性别，等等。你上面的真的是三只狗，而不是一只。为了代表他们，你应该有一个狗的集合 - 最好是像std::vector这样的标准集合，但如果你不被允许使用它（这可能是半合理的，因为这听起来似乎是家庭作业）至少是一个数组。
dog dogs[10]; // an array of 10 dogs (none yet initialized though)
dogs[0] = dog("Misty, 15, female");
dogs[1] = dog("Tristian, 12, male");
dogs[2] = dog("Tempest, 11, female");
猪，牛，马等几乎相同：一个动物对象应该代表一只真正的动物。动物的集合与单一动物不同。但是，请注意上面的评论：10只狗的阵列正好 - 10只狗（即使它们都没有名字，年龄或性别，我们已经定义它们所以它们都正式存在）。这意味着patient_count将在您定义数组时报告存在10只狗，无论包含有意义数据的数量是多少。这是std::vector显然是更好选择的一种方式。如果您执行以下操作：
std::vector<dog> dogs;
dogs.push_back("Misty, 15, female");
dogs.push_back("Tristian, 12, male");
dogs.push_back("Tempest, 11, female");
此时，您已经创建并存储了3只狗，因此如果您此时打印出patient_count，它应该显示3（表示创建/定义的实际狗）而不是10（或其他）代表潜在动物的数量，而忽略包含有意义数据的数字。
答案 2 :(得分：1)
在你的课程中，你宣称他们是以下3个函数的朋友（分别针对马，猪和狗类）
int patient_count(horse);
pig patient_count(pig);
dog patient_count(dog);
这些功能都不存在。唯一存在的功能就是这个：
int patient_count(horse,pig,dog);
使用该声明替换每个类中的朋友行。你还需要向前宣布猪和狗。
答案 3 :(得分：0)
由于
int patient_count(horse);
pig patient_count(pig);
dog patient_count(dog);
和
int patient_count(horse target_horse, pig target_pig, dog target_dog);
patient_count 重载。最好的方法是使用像这样的字段animal_count创建一个基类动物
/*******************************************************\
* Veternarian Class Problem - I need a class for each *
* of 3 animals. Horse, Pig and Dogs *
\*******************************************************/
#include <cstdlib>
#include <iostream>
#include <string>
const int HORSE_KENNEL = 100; // Number of horses we can store
const int PIG_KENNEL = 100; // Number of Pigs we can store
const int DOG_KENNEL = 100; // Number of Dogs we can store
class animal{
protected:
int animal_count;
public:
friend int patient_count(animal);
};
/*******************************************************\
* Class horse *
* *
* Member functions *
* animal_count -- Keeps track of the number of horses *
* add_horse -- Sends data into the object *
* next_horse -- returns data from the object *
\*******************************************************/
// Definition of the Class
class horse : public animal {
private:
std::string horse_data[HORSE_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
horse::horse( );
// A Function that accepts an argument but returns nothing
void add_horse(const std::string new_horse_data);
// This method returns the next Horse in the queue
std::string next_horse( );
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline horse::horse( )
{
for(int i = 0; i < HORSE_KENNEL; ++i){
horse_data[i] = "Empty Spot";
}
animal_count = 0; // Zero the data count
}
/*******************************************************\
* horse::add_horse -- Send data to Object *
\*******************************************************/
inline void horse::add_horse(const std::string new_horse_data)
{
horse_data[animal_count] = new_horse_data;
++animal_count;
}
/*******************************************************\
* horse::next_horse - get data from object *
\*******************************************************/
inline std::string horse::next_horse( )
{
// this is specifically implementing a queue
std::string current_horse = " ";
int target_horse = 0;
for(int i = 0;i < HORSE_KENNEL; ++i){
if(horse_data[i] != "Empty Spot"){
std::cout << "Horse Number " << i << " " << horse_data[i] << std::endl;
}
}
std::cout << "Select the horse you want: ";
std::cin >> target_horse;
return (horse_data[target_horse]);
}
/*******************************************************\
* Class Pig *
* *
* Member functions *
* animal_count -- Keeps track of the number of pigs *
* add_pig -- Sends data into the object *
* next_pig -- returns data from the object *
\*******************************************************/
// Definition of the Class
class pig :public animal{
private:
// Variable to keep track of data
std::string pig_data[PIG_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
pig::pig( );
// A Function that accepts an argument but returns nothing
void add_pig(const std::string new_pig_data);
// This method returns the next pig in the queue
std::string next_pig( );
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline pig::pig( )
{
for(int i = 0; i < PIG_KENNEL; ++i){
pig_data[i] = "Empty Spot";
}
animal_count = 0; // Zero the data count
}
/*******************************************************\
* pig::add_pig -- Send data to Object *
\*******************************************************/
inline void pig::add_pig(const std::string new_pig_data)
{
pig_data[animal_count] = new_pig_data;
++animal_count;
}
/*******************************************************\
* pig::next_pig - get data from object *
\*******************************************************/
inline std::string pig::next_pig( )
{
// this is specifically implementing a queue
std::string current_pig = " ";
int target_pig = 0;
for(int i = 0;i < PIG_KENNEL; ++i){
if(pig_data[i] != "Empty Spot"){
std::cout << "pig Number " << i << " " << pig_data[i] << std::endl;
}
}
std::cout << "Select the pig you want: ";
std::cin >> target_pig;
return (pig_data[target_pig]);
}
/*******************************************************\
* Class dog *
* *
* Member functions *
* animal_count -- Keeps track of the number of dogs *
* data_to_object -- Sends data into the object *
* data_from_object -- returns data from the object *
\*******************************************************/
// Definition of the Class
class dog :public animal {
private:
std::string dog_data[DOG_KENNEL]; // A Place to put the data
// Declarations for the method Prototypes
public:
// Initialize
dog::dog( );
// A Function that accepts an argument but returns nothing
void add_dog(const std::string new_dog_data);
// This method returns the next dog in the queue
std::string next_dog( );
};
/*******************************************************\
* Method Definition - Here we flush out the prototypes *
* outlined in the last section *
\*******************************************************/
inline dog::dog( )
{
for(int i = 0; i < DOG_KENNEL; ++i){
dog_data[i] = "Empty Spot";
}
animal_count = 0; // Zero the data count
}
/*******************************************************\
* dog::add_dog -- Send data to Object *
\*******************************************************/
inline void dog::add_dog(const std::string new_dog_data)
{
dog_data[animal_count] = new_dog_data;
++animal_count;
}
/*******************************************************\
* dog::next_dog - get data from object *
\*******************************************************/
inline std::string dog::next_dog( )
{
// this is specifically implementing a queue
std::string current_dog = " ";
int target_dog = 0;
for(int i = 0;i < DOG_KENNEL; ++i){
if(dog_data[i] != "Empty Spot"){
std::cout << "dog Number " << i << " " << dog_data[i] << std::endl;
}
}
std::cout << "Select the dog you want: ";
std::cin >> target_dog;
return (dog_data[target_dog]);
}
/**************************************************\
* This function is a friend of all the animal *
* classes and returns the total of all animals *
* PROBLEM ******* PROBLEM *********PROBLEM *********
* When I add the other 2 classes on the next line *
* The program stops working *
\**************************************************/
// int patient_count(horse target_horse) //works
int patient_count(animal target_animal) // Nova
{
int all_animals = target_animal.animal_count;
return (all_animals);
}
int patient_count(horse target_horse, pig target_pig, dog target_dog) // Nova
{
// int all_animals = target_horse.animal_count; //Works
int all_animals = patient_count(target_horse) + patient_count(target_pig) + patient_count(target_dog); // Nova
return (all_animals);
}
/**************************************************\
* The Class is defined above, this section is a *
* Small testing harness to verify that the class *
* is doing what it was designed to do *
\**************************************************/
int main( )
{
int total_animals;
horse current_horse; // Create a instance
// Send 3 values to the object
current_horse.add_horse("Mr Ed, 10, Male");
current_horse.add_horse("Lightning, 4, Female");
current_horse.add_horse("Blitz, 7, Male");
// Call for the return of the 3 values
std::cout << "Selected Horse ->" << current_horse.next_horse( ) << '\n';
pig current_pig; // Create a instance
// Send 3 values to the object
current_pig.add_pig("Arnold, 4, Male");
current_pig.add_pig("Babe, 2, Female");
current_pig.add_pig("Killer, 7, Male");
// Call for the return of the 3 values
std::cout << "Selected Pig ->" << current_pig.next_pig( ) << '\n';
dog current_dog; // Create a instance
// Send 3 values to the object
current_dog.add_dog("Misty, 15, Female");
current_dog.add_dog("Tristian, 12, Male");
current_dog.add_dog("Tempest, 11, Female");
// Call for the return of the 3 values
std::cout << "Selected Dog ->" << current_dog.next_dog( ) << '\n';
// Now get the results from the friend function
// total_animals = patient_count(current_horse); // Works
total_animals = patient_count(current_horse, current_pig, current_dog); // Nova
std::cout << "Total Animals: " << total_animals << std::endl;
return (0);
}