我的数据库的最终值在快速排序后损坏

Question

所以我设法编写了一个程序，将OpAmp数据存储在一个小型数据库（10条数据）中，一切似乎都很好，直到我执行快速排序，按压摆率升序排序。当我这样做时，数据库中的最后一条数据会以一系列与输入的数据无关的符号的形式返回。这不会发生在按名称快速排序时。有人知道出了什么问题吗？这是我的代码...

//File: Task1.cpp
//Title: Structured Programming in C++
//Created: 05/12/2012
//Author: Nicole ...
//ID Number: ...
//Accompanying Files: database.txt
//Description:A program which allows 
#include <iostream>
#include <fstream>
#include <string.h>
using namespace std;
// the format of each of the elements in the database
struct OpAmps {
  char Name[20];  // the name of the op-amp (e.g. "741")
  unsigned int PinCount;  // the number of pins in the package
  double SlewRate;  // the slew rate in volts per microsecond
};
// the length of the fixed array to be used for database - must be at least one
// and no greater the maximum value allowed in an unsigned long (see the file limits.h)
#define DATABASE_MAX 10
// file used for the database
#define DATABASE_FILENAME "database.txt"
// function prototypes
void Enter(OpAmps&, unsigned long&);
void Save(OpAmps[], unsigned long);
void Load(OpAmps[], unsigned long&);
void Sort(OpAmps[], unsigned long);
void Display(OpAmps[], unsigned long);
void QuickSortName (OpAmps[], unsigned long);
void QuickSortSlewRate (OpAmps[], unsigned long);
// Control the entering, saving, loading, sorting and displaying of elements in the database
// Arguments: None
// Returns: 0 on completion
int main()
{
  OpAmps OpAmp[DATABASE_MAX];   // the database
  unsigned long database_length = 0;  // the number of elements in the database
  char UserInput;
  // loop until the user wishes to exit
  while (1) {
    // show the menu of options
    cout << endl;
    cout << "Op-amp database menu" << endl;
    cout << "--------------------" << endl;
    cout << "1. Enter a new op-amp into the database" << endl;
    cout << "2. Save the database to disk" << endl;
    cout << "3. Load the database from disk" << endl;
    cout << "4. Sort the database" << endl;
    cout << "5. Display the database" << endl;
    cout << "6. Exit from the program" << endl << endl;
    // get the user's choice
    cout << "Enter your option: ";
    cin >> UserInput;
    cout << endl;
    // act on the user's input
    switch(UserInput) {
      case '1':
            Enter(OpAmp[database_length], database_length);
         break;
      case '2':
            Save(OpAmp, database_length);
        break;
      case '3':
            Load(OpAmp, database_length);
        break;
      case '4':
            Sort(OpAmp, database_length);
        break;
      case '5':
            Display(OpAmp, database_length);
        break;
      case '6':
        return 0;
      default:
            cout << "Invalid Entry" << endl << endl;
        break;
    }
  }
}
void Enter(OpAmps& eOpAmp, unsigned long& database_length)
{
    cout<<"1) Enter Data"<<endl;
        if (database_length == DATABASE_MAX)
        {
            cout <<endl << "Database is full!!!" << endl;
        }
        else
        {
            cout << endl << "Name of OpAmp: ";
            cin >> eOpAmp.Name;
            cout << endl << "Number of Pins on OpAmp: ";
            cin >> eOpAmp.PinCount;
            cout << endl << "Slew Rate of OpAmp: ";
            cin >> eOpAmp.SlewRate;
            cout << endl<< "All Items Added!" << endl << "Now Save Your Data!" << endl;
            database_length++;
        }
}
void Save(OpAmps sOpAmp[], unsigned long database_length)
{
    cout<<"2) Save Data"<<endl;
    fstream output_file; 
    output_file.open(DATABASE_FILENAME, ios::out);
    if (!output_file.good())
        {
            cout << "Error Loading File!!!" << endl;
            return;
        }
    else
        {
            int i;
            output_file << database_length<< endl<<endl;
            for(i=0;i<=database_length-1;i++)
        {
            output_file << sOpAmp[i].Name << endl; 
            output_file << sOpAmp[i].PinCount<< endl;
            output_file << sOpAmp[i].SlewRate;
        }
            cout << endl << "Data Saved" <<endl;
        }
    output_file.close();
}
void Load(OpAmps lOpAmp[], unsigned long& database_length)
{
    cout<<"3) Load Data"<<endl; 
    fstream input_file;
    input_file.open(DATABASE_FILENAME, ios::in);
    if (!input_file.good())
        {
            cout << "Error Loading File!!!" << endl;
            return;
        }
    else
        {
            input_file >> database_length;
            for(int i=0;i<=database_length-1;i++)
                {
                    input_file >> lOpAmp[i].Name; 
                    input_file >> lOpAmp[i].PinCount;
                    input_file >> lOpAmp[i].SlewRate;
                }
        }
    input_file.close();
}
void Sort(OpAmps qOpAmp[], unsigned long database_length)
{
  cout<<"4) Sort Data"<<endl;
  char UserInput;
  // show the menu of options
    cout << endl;
    cout << "Sorting options" << endl;
    cout << "---------------" << endl;
    cout << "1. To sort by name" << endl;
    cout << "2. To sort by slew rate" << endl;
    cout << "3. No sorting" << endl << endl;
    // get the user's choice of sorting operation required
    cout << "Enter your option: ";
    cin >> UserInput;
    // act on the user's input
    switch (UserInput) {
        case '1':
            cout <<"Sort By Name"<<endl;
            QuickSortName (qOpAmp, database_length);
        break;
        case '2':
            cout <<"Sort By Slew Rate"<<endl;
            QuickSortSlewRate (qOpAmp, database_length);
        break;
        case '3':
            cout <<"No Sort"<<endl;
        break;
        default:
            cout <<"Invalid Entry"<< endl;
            return;
        break;
    }
}
void QuickSortName (OpAmps nOpAmp[], unsigned long database_length)
{
    OpAmps temp;    // Local variable used to swap records
    for(int i=0; i<database_length; i++)
    {
        for(int i=0; i<database_length; i++)
        {
            if(strcmp(nOpAmp[i].Name, nOpAmp[i+1].Name)>0)
            {
                temp = nOpAmp[i];
                nOpAmp[i] = nOpAmp[i+1];
                nOpAmp[i+1] = temp;
            }
        }
    }
    Display (nOpAmp, database_length);
}
void QuickSortSlewRate (OpAmps rOpAmp[], unsigned long database_length)
{
    OpAmps temp;    // Local variable used to swap records
    for(int i=0; i<database_length; i++)
    {
        for(int i=0; i<database_length; i++)
        {
            if(rOpAmp[i].SlewRate > rOpAmp[i+1].SlewRate)
            {
                temp = rOpAmp[i];
                rOpAmp[i] = rOpAmp[i+1];
                rOpAmp[i+1] = temp;
            }
        }
    }
    Display (rOpAmp, database_length);
}

void Display(OpAmps dOpAmp[], unsigned long database_length)
{
    cout<<"5) Display Data"<<endl;
    if (database_length == 0)
    {
        cout<<endl<< "Database is Empty!!!" <<endl;
    }
    else
    {   
        cout <<endl<<database_length<<" items are in the database" << endl;
        for (unsigned long i = 0; i <= (database_length-1); i++)
        {
            cout << endl << "Database Entry Number: " << i+1<< endl;
            cout << "Name: " << dOpAmp[i].Name <<endl;
            cout << "PinCount: " << dOpAmp[i].PinCount<<endl;
            cout << "Slew Rate: " << dOpAmp[i].SlewRate<< endl <<endl;
        }
    }
}

输入每条数据后，

选择"保存"，然后输入下一段，输入任意数量的项目后，加载数据，然后对数据进行排序。您将看到此问题。任何帮助都可以消除此错误！

Answer 1

void QuickSortSlewRate (OpAmps rOpAmp[], unsigned long database_length)
{
    OpAmps temp;    // Local variable used to swap records
    for(int i=0; i<database_length; i++)
    {
        for(int i=0; i<database_length; i++)
        {

嵌套循环使用相同的变量 （i）。

if(rOpAmp[i].SlewRate > rOpAmp[i+1].SlewRate)

当 i 等于 （database_length - 1） 时，您将在此处离开数组的末尾。

void Save(OpAmps sOpAmp[], unsigned long database_length)
{
    ...
        for(i=0;i<=database_length-1;i++)
        {
            output_file << sOpAmp[i].Name << endl; 
            output_file << sOpAmp[i].PinCount<< endl;
            output_file << sOpAmp[i].SlewRate;         // **missing endl**
        }

您的文件格式可能已损坏 - 保存功能中缺少endl。

既然您使用的是C++，为什么不使用std::sort而不是慢速气泡排序呢？

// compare function for std::sort
bool CompareSlewRate(const OpAmps& a, const OpAmps& b)
{
    return a.SlewRate < b.SlewRate;
}
void QuickSortSlewRate (OpAmps rOpAmp[], unsigned long database_length)
{
    std::sort(rOpAmp, rOpAmp + database_length, CompareSlewRate);
    Display (rOpAmp, database_length);
}