從文件讀取到不同的類對象

Question

我是C++編程的初學者，我有一個關於從文件讀入特定類對象的問題，其中一個是數組。

我的類對象：

const int SIZE_OF = 5; 

class Student 
{ 
public: 
    Student(); 
    Student(const Student &); 
    Student(string, int, int, int, int, int); 
    friend std::istream& operator >> (std::istream& in, Student& S); 
    void display(); 
private: 
    string lastName; 
    int grades[SIZE_OF]; 
}; 

CPP文件來定義功能：

Student::Student() 
{ 
    int i; 
    string lastName = "default"; 
    for (i = 0; i < 5; i++) 
    { 
     grades[i] = 0; 
    } 
} 

Student::Student(const Student & S) 
{ 
    int i; 
    lastName = S.lastName; 
    for (i = 0; i < 5; i++) 
    { 
     grades[i] = S.grades[i]; 
    } 
} 

Student::Student(string S, int a, int b, int c, int d, int e) 
{ 
    lastName = S; 
    grades[0] = a; 
    grades[1] = b; 
    grades[2] = c; 
    grades[3] = d; 
    grades[4] = e; 
} 

std::istream& operator >> (std::istream& in, Student& S) 
{ 
    std::string line; 
    std::getline(in, line); 
    in >> S.lastName >> S.grades[0] >> S.grades[1] >> S.grades[2] >> S.grades[3] >> S.grades[4]; 
    getline(in, S.lastName); 
    return in; 
} 

void Student::display() 
{ 
    int i; 
    int sum = 0; 
    double average; 
    cout << "Last Name: " << lastName << endl; 
    cout << "Grades: " << endl; 
    for (i = 0; i < 5; i++) 
    { 
     cout << grades[i] << endl; 
    } 
    for (i = 0; i < 5; i++) 
    { 
     sum = sum + grades[i]; 
    } 
    average = sum/5; 
    cout << "Average: " << average;  
} 

我需要做的是從文件中讀取並保存Student類的lastName對象下的叫什麼名字。然後我需要將每個等級保存在數組對象中。然後，我需要爲下一個名稱創建一個新的Student類對象，併爲4個名稱重複該過程。我從閱讀的文件：

George 
75,85,95,100,44 
Peter 
100,100,100,100,100 
Frank 
44,55,66,77,88 
Alfred 
99,88,77,66,55 

Answer 1

您的以下功能似乎是錯誤的：

std::istream& operator >> (std::istream& in, Student& S) 
{ 
    std::string line; 
    std::getline(in, line); 
    in >> S.lastName >> S.grades[0] >> S.grades[1] >> S.grades[2] >> S.grades[3] >> S.grades[4]; 
    getline(in, S.lastName); 
    return in; 
} 

你讀的lastName兩次，你不要忽略「」性格...你可以試試這樣的：

std::istream& operator >> (std::istream& in, Student& S) 
{ 
    char dummy; 
    in >> S.lastName >> S.grades[0] 
     >> dummy >> S.grades[1] 
     >> dummy >> S.grades[2] 
     >> dummy >> S.grades[3] 
     >> dummy >> S.grades[4]; 

    return in; 
} 

UPDATE： 如果考慮內lastName的空間，你應該有改變的第一行使用std ::函數getline如下：

std::istream& operator >> (std::istream& in, Student& S) 
{ 
    char dummy; 
    std::getline(in, S.lastName) 
    in >> S.grades[0] 
     >> dummy >> S.grades[1] 
     >> dummy >> S.grades[2] 
     >> dummy >> S.grades[3] 
     >> dummy >> S.grades[4]; 
    in.ignore(); // remove last '\n' 
    return in; 
} 

然後：

int main() 
{ 
    Student s; 
    std::vector<Student> all; 

    while (cin>>s) 
     all.push_back(s); 
} 

... ...和足夠的更新！