【发布时间】：2011-07-01 19:18:37
【问题描述】：
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。我可以让功能成为 1 个班级的朋友，但不能成为所有 3 个班级的朋友。谁能告诉我我的错误是什么？
/*******************************************************\
* 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);
}
【问题讨论】：
-
写一个最小例子的方法！我认为您的函数签名与您的
friend声明不匹配。 -
@Kerrek：这是讽刺、讽刺还是赞美？
-
@Sehe：努力让未来的问题变得更可口，同时获得一些乐趣 :-)
-
@Nico：在某个地方使用虚函数可能会做得更好。通常，如果您发现自己说了很多
friend，说明有些地方不太对劲。 -
往好的方面看..现在你有一个免费的动物犬舍实现......
标签： c++ friend-function