如何從文件中讀取結構數組並對其進行排序？

Question

前言：教授設定的准則，我必須使用數組，而不是其他一些數據結構。 我們應該遵循的方法的偽代碼（不是很簡潔）：

name and grade are read into a temporary location
loop from the end of the filled part of the array down to beginning {
if (new last name < current last name) {
   copy current name and grade down
}
else if (new/current last names are equal and new first name < current first name) {
   copy/assign current name and grade down
}
else {
   found right place, break out of loop
}
}
now that you've made room, insert (copy) new name into correct sorted position

我看到我可能試圖讀取數組位置[-1]來打破數組界限，但是我想不出一種避免這種情況的方法，因為我是從已有的項目數中倒數，並且必須比較它們。

我正在從文本文件中讀取行，並將每一行的片段存儲到結構中。 然后，我使用一種插入排序式算法來按字母順序存儲結構。 但是，我的數組似乎並沒有用新行來填充前幾行，而只是覆蓋了前幾行……這似乎是我的一個比較測試失敗了，因為我的復制位置似乎從未改變，盡管這可能是因為初始數組填充在某種程度上失敗了。 我覺得很愚蠢，我必須缺少一些簡單的東西...而且，我的DisplayList模塊顯然也永遠不會獲得填充了任何東西的數組。 我是否以錯誤的方式更改了陣列？

這是有問題的模塊：

bool sortInput(ifstream &infile, StudentType students[], int size)
{
   StudentType temp;
   int copyToHere;

   if(size == 0)
   {
      infile >> temp.last >> temp.first >> temp.grade;
      strcpy(students[0].last, temp.last);
      strcpy(students[0].first, temp.first);
      students[0].grade = temp.grade;
      size++;
   } 

   while(infile)
   {
      infile >> temp.last >> temp.first >> temp.grade;
      //cout << "TEST" << temp.last << temp.first << temp.grade << endl;

      for(int i = size; i > 0; i--)
      {       
         if(strcmp(temp.last, students[i-1].last) < 0)
         {
            students[i] = students[i-1];
            students[i-1] = temp;
         }
         else if(strcmp(temp.last, students[i].last) == 0 && strcmp(temp.first, students[i].first) < 0)
         {
            students[i] = students[i-1];
         }
         else
         {
            break;
         }

         copyToHere = i;
      }

      cout << "Size = " << size << " and copy position = " << copyToHere << endl;
      students[copyToHere] = temp;
      size++;

      //test to see if array is populated properly
      for(int i = 0; i < size; i++)
      {
         cout << "Name is " << students[i].first << " " << students[i].last << " and grade is " << students[i].grade << endl;
      }

      cout << "DONE" << endl;

   } //end while loop

   return true;
}

這是完整的代碼（如有必要，無論出於何種原因或其他情況）：

// ----------------------------------------------------------------------------
// You write meaningful doxygen comments and assumptions

#include <string.h>
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;

int const MAXSIZE = 100;            // maximum number of records in total
int const MAXLENGTH = 31;           // maximum string length 
int const MAXGRADE = 100;           // highest possible grade
int const LOWGRADE = 0;             // lowest possible grade
int const GROUP = 10;               // group amount
int const HISTOGRAMSIZE = (MAXGRADE-LOWGRADE)/GROUP + 1;    // grouped by GROUP

struct StudentType  {               // information of one student
   int grade;                       // the grade of the student
   char last[MAXLENGTH];            // last name (MAXLENGTH-1 at most)
   char first[MAXLENGTH];           // first name (MAXLENGTH-1 at most)
};

// prototypes go here
bool sortInput(ifstream &, StudentType [], int);
void displayList(StudentType [], int);
/*setHistrogram();
displayHistogram();
findAverage();*/

//------------------------------- main ----------------------------------------
int main()  {
   StudentType students[MAXSIZE];   // list of MAXSIZE number of students
   int size = 0;                    // total number of students
   int histogram[HISTOGRAMSIZE];    // grades grouped by GROUP
   int average = 0;                 // average exam score, truncated

   // creates file object and opens the data file
   ifstream infile("data1.txt");
   if (!infile)  { 
      cout << "File could not be opened." << endl; 
      return 1;  
   }

   // read and sort input by last then first name
   bool successfulRead = sortInput(infile, students, size);              

   // display list, histogram, and class average 
   if (successfulRead)  {
      displayList(students, size);
     // setHistogram(... you figure parameters ...);
     // displayHistogram(... you figure parameters ...);
     // average = findAverage(... you figure parameters ...);
      cout << "Average grade: " << average << endl << endl;
   }
   return 0;
}

bool sortInput(ifstream &infile, StudentType students[], int size)
{
   StudentType temp;
   int copyToHere;

   if(size == 0)
   {
      infile >> temp.last >> temp.first >> temp.grade;
      strcpy(students[0].last, temp.last);
      strcpy(students[0].first, temp.first);
      students[0].grade = temp.grade;
      size++;
   } 

   while(infile)
   {
      infile >> temp.last >> temp.first >> temp.grade;
      //cout << "TEST" << temp.last << temp.first << temp.grade << endl;

      for(int i = size; i > 0; i--)
      {       
         if(strcmp(temp.last, students[i-1].last) < 0)
         {
            students[i] = students[i-1];
            students[i-1] = temp;
         }
         else if(strcmp(temp.last, students[i].last) == 0 && strcmp(temp.first, students[i].first) < 0)
         {
            students[i] = students[i-1];
         }
         else
         {
            break;
         }

         copyToHere = i;
      }

      cout << "Size = " << size << " and copy position = " << copyToHere << endl;
      students[copyToHere] = temp;
      size++;

      //test to see if array is populated properly
      for(int i = 0; i < size; i++)
      {
         cout << "Name is " << students[i].first << " " << students[i].last << " and grade is " << students[i].grade << endl;
      }

      cout << "DONE" << endl;

   } //end while loop

   return true;
}

void displayList(StudentType students[], int size)
{
   cout << "List of names sorted:" << endl;

   for(int i = 0; i < size; i++)
   {
      cout << " " << students[i].grade << " " << students[i].last << " " << students[i].first << endl;
   }
}

// ----------------------------------------------------------------------------
// functions with meaningful doxygen comments and assumptions go here

Answer 1

您的插入排序實際上沒有正確插入。 讓我們看一下主插入循環的一部分：

   if(strcmp(temp.last, students[i-1].last) < 0)
     {
        students[i] = students[i-1];
        students[i-1] = temp;
     }

這樣做的目的顯然是將temp插入位置i-1處的數組中。 您正在將i-1處的項移動到i但是數組中其他元素發生了什么？ 您需要將它們全部上移一個位置，以便為插入的元素騰出空間。 就像是：

memmove(students + i, students + i - 1, sizeof(students[0]) * size - i - 1);

您的代碼中也有其他問題。 copyToHere可能未初始化。 您要多次將temp復制到數組中（ students[i-1] = temp;和students[copyToHere] = temp;都不需要）。 一旦完成內循環的插入，就應該開始操作。 當列表為空時，您不需要進行特殊處理，依此類推。

看一下插入排序算法的偽代碼 ，看看是否可以簡化並重寫以消除問題。

Answer 2

解決我自己的問題哈哈。 我因沒有正確完成else語句而感到愚蠢。 現在，我正在嘗試重做我的名字比較，因為出現問題是因為它不會按字母順序排列相同的姓氏。

經驗教訓：在認為您被分叉之前，請認真研究所有內容。 現在我真的感覺自己像個白痴，希望不會浪費很多窺視時間。

  for(int i = size; i > 0; i--)
  {       
     if(strcmp(temp.last, students[i-1].last) < 0)
     {
        students[i] = students[i-1];
        students[i-1] = temp;
     }
     else if(strcmp(temp.last, students[i].last) == 0 && strcmp(temp.first, students[i].first) < 0)
     {
        students[i] = students[i-1];
        students[i-1] = temp;
     }
     else
     {
        students[i] = temp;
        break;
     }

     insertHere = i;
  }