C++：錯誤'std :: string'是私人的

Question

因此，對於課程，我必須編寫一個模擬賽馬的程序。這是我們第一個涉及課程的重大項目。我被卡在主題中提到的錯誤。現在，自引入它們以來，我一直在與指針進行鬥爭，所以我毫不懷疑這是我的總體問題所在。我已經請教過我的教授，但他沒有回覆我的電子郵件。我也聯繫過朋友等，沒有人回到我身邊。

這是我的頭文件（Horse.h）：

#ifndef HORSE_H 
#define HORSE_H 
#include <string> 

class Horse 
{ 
    private: 
    std::string name; 
    std::string jockey; 
    int maxSpeed; 
    int distanceTraveled; 
    int racesWon; 
    public: 
    Horse(std::string, std::string); 
    void runOneSecond(int); 
    void sendToGate(); 
    void displayHorse (double); 
}; 

#endif // HORSE_H 

這裏是我的Horse.cpp：

#include <iostream> 
#include <string> 
#include <stdlib.h> 
#include <time.h> 
#include "Horse.h" 
using namespace std; 

Horse::Horse(string name, string jockey) 
{ 
    srand (time(NULL)); 
    int maxSpeed = rand() % 30 + 1; 
    distanceTraveled = 0; 
}; 

void Horse::runOneSecond(int maxSpeed) 
{ 
    srand (time(NULL)); 
    distanceTraveled = rand() % maxSpeed; 
}; 

void Horse::sendToGate() 
{ 
    distanceTraveled = 0; 
}; 

void Horse::displayHorse(double raceDistance) 
{ 
    int percentage; 
    for (int i = 0; i < numberOfHorses; i++) 
    { 
    cout << "|"; 

    } 
}; 

這裏是我的main.cpp：

#include <iostream> 
#include <string> 
#include <cctype> 
#include "Horse.h" 
using namespace std; 

int main() 
{ 
    double raceDistance = 0; 
    int numberOfHorses = 0; 
    char choice = 'Y'; 
    string name; 
    string jockey; 


    cout << "Enter the number of horses for the race: "; 
    cin >> numberOfHorses; 
    Horse** horsePtr = new Horse* [numberOfHorses]; 


// Trouble section. 
    for (int i = 0; i < numberOfHorses; i++) 
    { 
    cout << "Fill in the name of the horse: "; 
    cin >> horsePtr[i]->name; 
    cout << "Fill in the name of the jockey: "; 
    cin >> horsePtr[i]->jockey; 
    } 

    cout << "How long should the race be (in meters): "; 
    cin >> raceDistance; 

    cout << endl; 
    cout << "Start!" << endl; 

    for (int i = 0; i < numberOfHorses; i++) 
    { 
    horsePtr[i]->sendToGate(); 
    } 

    for (int i = 0; i < numberOfHorses; i++) 
    { 
    horsePtr[i]->displayHorse(raceDistance); 
    } 

    cout << "Show the next second of the race? "; 
    cin >> choice; 

    while(toupper(choice) == 'Y') 
    { 
    if (toupper(choice) == 'Y') 
    { 
     for (int i = 0; i < numberOfHorses; i++) 
     { 
     horsePtr[i]->runOneSecond(maxSpeed); 
     horsePtr[i]->displayHorse(raceDistance); 
     } 
    } 
    } 

    return 0; 
} 

以下是錯誤：

Horse.cpp: In member function ‘void Horse::displayHorse(double)’: 
Horse.cpp:29:23: error: ‘numberOfHorses’ was not declared in this scope 
    for (int i = 0; i < numberOfHorses; i++) 
       ^
In file included from main.cpp:4:0: 
Horse.h: In function ‘int main()’: 
Horse.h:8:17: error: ‘std::string Horse::name’ is private 
    std::string name; 
       ^
main.cpp:25:25: error: within this context 
    cin >> horsePtr[i]->name; 
         ^
In file included from main_dmj8t6.cpp:4:0: 
Horse.h:9:17: error: ‘std::string Horse::jockey’ is private 
    std::string jockey; 
      ^
main.cpp:27:25: error: within this context 
    cin >> horsePtr[i]->jockey; 
         ^
main.cpp:55:35: error: ‘maxSpeed’ was not declared in this scope 
     horsePtr[i]->runOneSecond(maxSpeed); 
           ^

Answer 1

您不能訪問class的private成員。在你的例子，你的Horse類包含5 private members：

class Horse 
{ 
    private: 
    std::string name; 
    std::string jockey; 
    int maxSpeed; 
    int distanceTraveled; 
    int racesWon; 
public: 
}; 

這些private成員可以包括在Horse類方法中進行訪問，並通過任何friend類;然而：什麼也沒有其他人可以訪問它們。

int main() 
{ 
// Trouble section. 
    for (int i = 0; i < numberOfHorses; i++) 
    { 
    cout << "Fill in the name of the horse: "; 
    cin >> horsePtr[i]->name; <-- 
    cout << "Fill in the name of the jockey: "; 
    cin >> horsePtr[i]->jockey; <-- 
    } 
} 

在兩行標記，您試圖訪問的Horse的private成員和編譯器不會允許它。

考慮將這些變量public到Horse，或提供setter函數爲他們：

class Horse 
{ 
    private: 
    std::string name; 
    std::string jockey; 
    int maxSpeed; 
    int distanceTraveled; 
    int racesWon; 
public: 
    void SetName(std::string s) { name = s; } 
    void SetJockey(std::string s) { jockey = s; } 
}; 

int main() 
{ 
    std::string jockeyName; 
    std::cout << "Enter a name for the jockey: "; 
    std::cin >> jockeyName; 
    Horse* h = new Horse; 
    h->SetJockey(jockeyName); 
} 

您提供public構造函數Horse採用兩個std::string，但（無論您正在使用），所以你可以只傳遞相關信息給Horse：

Horse::Horse(std::string n, std::string j) : name(n), jockey(j) 
{ 
    // Other things... 
} 

int main() 
{ 
    Horse* h = new Horse("Phar Lap", "Jim Pike"); 
} 

請注意，我的兩個例子都只是符合你的c urrent代碼。如果需要，應將其替換爲std::vector和指針（或std::shared_ptr，以符合您的需求爲準）。