按特定值排序struct-members

Question

我已經有一段時間了現在這個問題，所以我認爲這將是更好的要求方向。嘗試搜索，沒有任何幫助，現在正在努力爭取這麼長時間，所以我們走了。

我正在學習C++，並且在這個練習中遇到了很多困難：我必須使用struct保存3位學生的詳細信息，然後按照他們與學校的距離以升序排列。第一名學生的詳細信息由用戶輸入提問，其他人則通過變量進行初始化。一切都很好，直到我必須把它們整理出來。

此刻，我試圖將數組傳遞給排序函數，其中包含每個學生的詳細信息，我手動輸入該數組以供測試。當我試圖直接從struct成員值初始化數組，然後將該數組傳遞給sort func時，我遇到了一些嚴重的問題。另外，在這個練習中，我必須使用C數組。

Perpaps有人可以告訴我這樣做的正確方法嗎？也許有更簡單的方法來做到這一點？提前致謝！這裏是我的代碼：

編輯：平臺：Windows 7中，IDE：Visual Studio的2013

#include <iostream> 
#include <algorithm> 
#include <functional> 

using namespace std; 

struct personaldata { 
    char firstname[50], lastname[50], address[50], postal[50]; 
    double distschool; 
    int shoesize; 
}; 

struct SortRecordsAscending 
{ 
    bool operator()(const personaldata& lhs, const personaldata& rhs) 
    { 
     return (lhs.distschool < rhs.distschool); 
    } 
}; 

void SortingObjectsExample(personaldata *details, int SIZE) 
{ 
    sort(details, details + SIZE, SortRecordsAscending()); 
    for (int i = 0; i < SIZE; ++i) 
    { 
     cout << details[i].firstname << " " << details[i].lastname << endl; 
     cout << details[i].address << " " << details[i].postal << endl; 
     cout << "Distance from school: " << details[i].distschool << endl; 
     cout << "Shoe size: " << details[i].shoesize << endl; 
     cout << endl; 
    } 
} 

int main() { 

    personaldata student1, student2, student3; 
    const int SIZE(3); // Amount of students 


    //Student 1 
    cout << "Enter first name: "; 
    cin.getline(student1.firstname, 50); 

    cout << "Enter last name: "; 
    cin.getline(student1.lastname, 50); 

    cout << "Enter distance from school: "; 
    cin >> student1.distschool; 
    cin.ignore(); 

    cout << "Enter address: "; 
    cin.getline(student1.address, 50); 

    cout << "Enter postal: "; 
    cin >> student1.postal; 

    cout << "Enter shoe size: "; 
    cin >> student1.shoesize; 

    //Student 2 
    strcpy_s(student2.firstname, 50, "Olli"); 
    strcpy_s(student2.lastname, 50, "Oppilas"); 
    student2.distschool = 9.4; 
    strcpy_s(student2.address, 50, "Opiskelijakatu 5a 14"); 
    strcpy_s(student2.postal, 50, "40200"); 
    student2.shoesize = 39; 

    //Student 3 
    strcpy_s(student3.firstname, 50, "Ossi"); 
    strcpy_s(student3.lastname, 50, "Oppilas"); 
    student3.distschool = 8.4; 
    strcpy_s(student3.address, 50, "Koululaiskatu 18b 2"); 
    strcpy_s(student3.postal, 50, "40100"); 
    student3.shoesize = 41; 

    personaldata details[3] = { 
      { "Oiva", "Oppilas", "Koivukatu 8B 16", "40100", 9.7, 43 }, 
      { "Ossi", "Oppilas", "Koululaiskatu 18b 2", "40100", 8.4, 41 }, 
      { "Olli", "Oppilas", "Lehtitie 3B 15", "401200", 8.7, 38 } 
    }; 

    SortingObjectsExample(details, SIZE); 

} 

上面的代碼工作，我希望它的方式。但是，如果我這樣做：

personaldata details[3] = { 
     { student1.firstname, "Oppilas", "Koivukatu 8B 16", "40100", 9.7, 43 }, 
     { student2.firstname, "Oppilas", "Koululaiskatu 18b 2", "40100", 8.4, 41 }, 
     { student3.firstname, "Oppilas", "Lehtitie 3B 15", "401200", 8.7, 38 } 
}; 

SortingObjectsExample(details, SIZE); 

我從編譯器

1>------ Build started: Project: Harj17, Configuration: Debug Win32 ------ 
1> harj17.cpp 
1>harj17.cpp(80): error C2440: 'initializing' : cannot convert from 'char (*)[50]' to 'char' 
1>There is no context in which this conversion is possible 
1>harj17.cpp(80): warning C4244: 'initializing' : conversion from 'double' to 'char', possible loss of data 
1>harj17.cpp(80): error C2440: 'initializing' : cannot convert from 'char [50]' to 'char' 
1>   There is no context in which this conversion is possible 
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== 

如果使用指針像這樣得到：

personaldata details[3] = { 
     { *student1.firstname, "Oppilas", "Koivukatu 8B 16", "40100", 9.7, 43 }, 
     { *student2.firstname, "Oppilas", "Koululaiskatu 18b 2", "40100", 8.4, 41 }, 
     { *student3.firstname, "Oppilas", "Lehtitie 3B 15", "401200", 8.7, 38 } 
}; 

它將編譯程序，但有警告消息，並不能正常工作，只能打印出人名的第一個字母。

1>------ Build started: Project: Harj17, Configuration: Debug Win32 ------ 
1> harj17.cpp 
1>harj17.cpp(80): warning C4244: 'initializing' : conversion from 'double' to 'char', possible loss of data 
1> Harj17.vcxproj -> Harj17.exe 
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ========== 

這是運行程序時的輸出。你可以看到問題的名稱和其他信息也搞砸了。

Enter first name: Example 
Enter last name: Student 
Enter distance from school: 13.37 
Enter address: Example Address 6B 16 
Enter postal: 1337 
Enter shoe size: 43 
EOppilas Koivukatu 8B 16 
40100 + 
Distance from school: 0 
Shoe size: 0 

OOppilas Koululaiskatu 18b 2 
40100) 
Distance from school: 0 
Shoe size: 0 

OOppilas Lehtitie 3B 15 
401200& 
Distance from school: 0 
Shoe size: 0 

Answer 1

很奇怪你可以使用STL算法，但不能使用數據結構。我不清楚你的問題，你有什麼困難。排序結構或構建它們？在任何情況下，這都是創建和分類結構的簡單方法。由於你的排序功能不需要任何狀態，它不需要是一個函子。它可以是一個正常的功能。

爲了進一步提高這一點，我會使用一個向量，將流操作符添加到結構並使用構造函數。

#include <algorithm> 
using namespace std; 

struct henkilotiedot { // Person first name, last name, address and postal 
    string etunimi, sukunimi, osoite, postinumero; 
    double koulumatka; // Distance from school 
    int kengannumero; // Shoe size 
}; 

bool SortByDistance(const henkilotiedot& lhs, const henkilotiedot& rhs) 
{ 
    return lhs.koulumatka < rhs.koulumatka; 
} 

int main() 
{ 
    const int SIZE = 3; 
    henkilotiedot data[] = { { "blah", "blah", "blah", "blah", 5.0, 10 }, { "blah", "blah", "blah", "blah", 1.0, 10 }, { "blah", "blah", "blah", "blah", 15.0, 10 } }; 
    sort(data, data + SIZE, SortByDistance); 
}