我的結構數組打印出垃圾

Question

我正在寫一個程序，它使用文件I/O接收輸入文件並將數據存儲在文件中的結構數組中。請記住，我爲您提供了部分代碼。不是全部。我知道一切都正常，因爲我輸入數據後打印出所有結構數組。在我嘗試對它進行排序之前，正在打印的垃圾發生在函數中。我試圖對其進行排序的函數在我的讀取文件函數中調用，在該函數中打印了結構數組。在那裏，它打印完美。當它調用sort函數時，結構數組會輸出垃圾。

---

這是我已經使用輸入文件的一個例子：

### building room_number capacity 
SAL 210 30 
OHE 100 120 
OHE 120 50 

### ID prefix course# sect# #minutes #mtgsperweek #students 
20001 CSCI 101 01 110 2 40 
20002 CSCI 101 02 110 2 60 
20003 CSCI 101 03 110 2 100 
20004 CSCI 103 01 90 2 50 
20005 CSCI 103 02 90 2 50 
20006 CSCI 103 03 90 2 75 
20007 CSCI 104 01 80 2 50 
20008 CSCI 104 02 80 2 50 
20009 CSCI 109 01 90 1 25 
20010 CSCI 109 02 90 1 25 
20011 CSCI 109 03 90 1 25 
20012 CSCI 109 04 90 1 25 

### ID days_constraint start_constraint end_constraint 
20001 MW 1000 1400 
20002 MW 1000 1400 
20003 TR 1000 1400 
20004 TR 0800 1200 
20005 TR 0800 1200 
20006 TR 0800 1200 
20007 MW 0800 1200 
20008 MW 0800 1200 
20009 M 0800 1200 
20010 M 0800 1200 
20011 T 0800 1200 
20012 T 0800 1200 

---

我在我讀取文件並輸入數據到結構的陣列的功能使用stringstream。我知道程序的一部分是正確的，因爲我之後打印出結構數組，並且它們都完美地打印出來。當我在我的read_File函數中調用一個新函數時，出現了這個問題，該函數稱爲sort_ByClassroomSize，其中我嘗試按教室容量以降序對結構數組進行排序。

---

下面是結構：

struct Room { 
    char building_code[4]; 
    int room_number; 
    int max_students; 
}; 

我聲明指針並根據房間用戶輸入的數目以後動態地分配。

  struct Room* roomsPtr; 

     roomsPtr = new struct Room[room_size]; 

其中room_size是一個計數器，用於統計宣佈房間的行數。

下面是我輸入數據到結構：

if(!(line[0] == '-' && line[1] == '-')) { 
     stringstream ss; 
     ss << line; 
     ss >> roomsPtr[i].building_code; 
     ss >> roomsPtr[i].room_number; 
     ss >> roomsPtr[i].max_students; 
     if(ss.fail()) { //checks format; terminates program if incorrect. 
     cout << "The file has been formatted incorrectly." << endl; 
     return; 
     } 

     //prints lines in section 1. 
     cout << roomsPtr[i].building_code << " " << roomsPtr[i].room_number << 
      " " << roomsPtr[i].max_students << endl; 

---

問題是在排序功能腳麻：

void order_ClassroomsBySize(int num_rooms) { //arranges classrooms in descending order 
    by classroom size 
     struct Room temp_value; 

       //prints the array of structs before arrangement 
     cout << endl; 
      cout << "Arranged classrooms in descending order by classroom size: " << endl; 
     for(int i = 0; i < num_rooms; i++) { 
      cout << roomsPtr[i].building_code << " " << roomsPtr[i].room_number << " " 
      << roomsPtr[i].max_students; 
      cout << endl; 
     } 
    } 
     //arranges the array of structs in descending order by classroom size 
     for(int i = 0; i < num_rooms; i++) { 
      for(int j = 0; j < num_rooms - 1; j++) { 
       if(roomsPtr[j].max_students < roomsPtr[j+1].max_students) { 
        temp_value = roomsPtr[j]; 
        roomsPtr[j] = roomsPtr[j+1]; 
        roomsPtr[j+1] = temp_value; 
       } 
      } 
     } 

     //prints the array of structs after arrangement 
     cout << endl; 
      cout << "Arranged classrooms in descending order by classroom size: " << endl; 
     for(int i = 0; i < num_rooms; i++) { 
      cout << roomsPtr[i].building_code << " " << roomsPtr[i].room_number << " " 
      << roomsPtr[i].max_students; 
      cout << endl; 
     } 
    } 

---

我的程序打印出如下：

### building room_number capacity 
SAL 210 30 
OHE 100 120 
OHE 120 50 


### ID prefix course# sect# #minutes #mtgsperweek #students 
20001 CSCI 101 01 110 2 40 
20002 CSCI 101 02 110 2 60 
20003 CSCI 101 03 110 2 100 
20004 CSCI 103 01 90 2 50 
20005 CSCI 103 02 90 2 50 
20006 CSCI 103 03 90 2 75 
20007 CSCI 104 01 80 2 50 
20008 CSCI 104 02 80 2 50 
20009 CSCI 109 01 90 1 25 
20010 CSCI 109 02 90 1 25 
20011 CSCI 109 03 90 1 25 
20012 CSCI 109 04 90 1 25 

### ID days_constraint start_contsraint end_constraint 
20001 MW 1000 1400 
20002 MW 1000 1400 
20003 TR 1000 1400 
20004 TR 0800 1200 
20005 TR 0800 1200 
20006 TR 0800 1200 
20007 MW 0800 1200 
20008 MW 0800 1200 
20009 M 0800 1200 
20010 M 0800 1200 
20011 T 0800 1200 
20012 T 0800 1200 

Arranged classrooms in descending order by classroom size: 
course# sect# #minutes OHE 593851250 1667592992 
t# #minutes OHE 1970170221 544433524 
OHE 120 50 

Arranged classrooms in descending order by classroom size: 
course# sect# #minutes OHE 593851250 1667592992 
t# #minutes OHE 1970170221 544433524 
OHE 120 50 

Answer 1

不知道，但部分問題可能是這幾行：

cout << "Arranged classrooms in descending order by classroom size: " << endl; 
for (std::set<Room>::iterator i = rooms.begin(); i != rooms.end(); i++) 
{ 
    cout << i->building_code << " " << i->room_number << " " 
     << i->max_students; 
     cout << endl; 

} 

特別是：

cout << i->building_code << " " << i->room_number << " " 
     << i->max_students; 

通過寫cout << i->building_code，你告訴cout打印出無論是在那char數組，即i->building_code。但是cout不知道數組有多大，所以它不斷打印出它看到的東西，直到達到空字符（char a = 0）。這會導致cout在打印內容時超出字符數組的邊界。

修復，這可能是使i->building_code 5個字節數組，而不是一個4字節數組，並填充結構之前歸零陣列的出路：

for (int j = 0; j < num_rooms; j++) 
    for (int i = 0; i < 5; i++) 
     roomPtr[j]->building_code[i] = 0; 

參見本頁約C-strings（字符數組以空字節結尾）以獲取更多信息。

此外，該代碼段：

//arranges the array of structs in descending order by classroom size 
    for(int i = 0; i < num_rooms; i++) { 
     for(int j = 0; j < num_rooms - 1; j++) { 
      if(roomsPtr[j].max_students < roomsPtr[j+1].max_students) { 
       temp_value = roomsPtr[j]; 
       roomsPtr[j] = roomsPtr[j+1]; 
       roomsPtr[j+1] = temp_value; 
      } 
     } 
    } 

應該是這樣的：

for(int i = 0; i < num_rooms - 1; i++) { 
     for(int j = i + 1; j < num_rooms; j++) { 
      if(roomsPtr[i].max_students < roomsPtr[j].max_students) { 
       temp_value = roomsPtr[i]; 
       roomsPtr[i] = roomsPtr[j]; 
       roomsPtr[j] = temp_value; 
      } 
     } 
    } 

如果你打算爲Selection Sort Algorithm（就像我認爲你是）。

Answer 2

與許多人所說的一樣，您在代碼中使用了兩種非常不同的範例：您使用的是C++，就像是C一樣。如果您真的使用C++，則可以使用更簡單的方法。

在習慣上，如果我在C++中，我會簡單地使用運算符重載。

像這樣：

class Room { 
    // not generally a good idea to have public members, but if you must... 
    public: 
     std::string building_code; 
     int room_number; 
     int max_students; 
     bool operator == (const Room & other) { 
      if (max_students != other.max_students) 
      { 
       return false; 
      } 
      else return room_number == other.room_number && building_code == other.building_code; 
     } 
     bool operator < (const Room & other) { 
      // returning the oposite to ensure descending order. 
      return max_students > other.max_students; 
     } 

}; 

然後，你可以只把你Room對象在std::set，這兩個動態您需要的所有客房，分配足夠的內存和讓他們沒有排序，像這樣：

#include <set> 

std::set<Room> rooms; 
room.insert(/* populate a room and put it here */); 
room.insert(/* populate a room and put it here */); 

這樣你就可以只輸出他們像這樣：

cout << "Arranged classrooms in descending order by classroom size: " << endl; 
for (std::set<Room>::iterator i = rooms.begin(); i != rooms.end(); i++) 
{ 
    cout << i->building_code << " " << i->room_number << " " 
     << i->max_students; 
     cout << endl; 

} 

我學到的關於C++的一切，我可能從here瞭解到。