缺少数组元素问题

Question

This is part of a homework assignment I recently finished. I am required to use an array of structs to store a library of books by title and author. The code is working and running perfectly fine when sorting and displaying author or title alphabetically according to user input.

The only issue I run into is when it shows all books sorted alphabetically. There are 14 books total in the text file used with the assignment, but only 13 books show up when the show all (S) option is entered.

An example of the error would be:

()

Audio for Games (Brandon)

Instead of:

Audio for Games (Brandon)
Beginning LINUX Programming (Stones and Matthew)

My Code:

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>

using namespace std;

// structure
struct Book {
    string title;
    string author;
};

const int ARRAY_SIZE = 1000;
Book books[ARRAY_SIZE];
string pathName;
ifstream lib;

// global variables
int loadData();
void showAll(int count);
void sortByTitle(int count, string title);


int main()
{
    // initialised variables
    int count = 0;
    char selector = 'q', yesNoAnswer = 'n';
    string name;
    string title;

    // asks user for file pathname
    cout << "Welcome to Tommy's Library Database." << endl;
    cout << "Please enter the name of the file: ";
    getline(cin, pathName);
    loadData();
    count = loadData();
    cout << count << " Records loaded successfully." << endl;
    // Switch case menu
    do {
        cout << endl << "Please enter a keyword that corresponds to the list of options: " << endl;
        cout << " Search by: (A)uthor, (T)itle, (S)how All, (Q)uit Program: ";
        cin >> selector;
        selector = toupper(selector);
        switch (selector)
        {
        case 'S':
            sortByTitle(count, title);
            if (count <= 0) {
                cout << " No counts found! " << endl;
            }
            else {
                showAll(count);
            }
            break;
        }
    }
    while (selector != 'q' && selector != 'Q');
    return 0;
}

int loadData()
{
    int count = 0;
    int i = 0;

    lib.open(pathName);
    ifstream lib(pathName);

    if (!lib)
    {
        cout << " Unable to open file path! " << endl;
        return -1;
    }
    while (!lib.eof())
    {
        getline(lib, books[count].title);
        getline(lib, books[count].author);
        count++;
    }
    return count;
}
// displays all book titles beside the author names
void showAll(int count)
{
    for (int i = 0; i < count; i++)
    {
        cout << books[i].title << " " << "(" << books[i].author << ")" << endl;
    }
}
// Sorts by book title.
void sortByTitle(int count, string title) {
    Book temp;
    for (int i = 0; i < count; i++) {
        for (int j = 0; j < count - i; j++) {
            if (books[j].title > books[j + 1].title) {
                temp = books[j];
                books[j] = books[j + 1];
                books[j + 1] = temp;
            }
        }
    }
}

The text file im using with the assignment (books.txt)

Objects First with Java
Barnes and Kolling
Game Development Essentials
Novak
The Game Maker's Apprentice
Overmars
C++ Programming: From Problem Analysis...
Malik
C++ Programming Lab Manual
Scholl
Beginning LINUX Programming
Stones and Matthew
C++ Programming: Program Design Including...
D. S. Malik
C++ How to Program
Deitel and Deitel
Programming and Problem Solving with C++
Dale, Weems, Headington
Game Character Development with Maya
Ward
Developing Games in Java
Brackeen
C# Programming
Harvey, Robinson, Templeman, Watson
Java Programming
Farrell
Audio for Games
Brandon

Answer 1

当您的书籍数组从 1 开始时，您在showAll()方法中从 0 开始循环，只需从 1 开始循环并转到 count + 1

for (int i = 1; i < count + 1; i++)

Answer 2

Your sort function doesn't work correctly. It's off by one and moves an empty element to the first index. It would cause undefined behavior if your array were full. Your sort function sorts all elements from 0 to count but it should sort from 0 to count - 1 . You should fix your sort function ( std::sort usually is faster than bubble sort):

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>

using namespace std;

// structure
struct Book {
    string title;
    string author;
};

const int ARRAY_SIZE = 1000;
Book books[ARRAY_SIZE];
string pathName;
ifstream lib;

// global variables
int loadData();
void showAll(int count);
void sortByTitle(int count, string title);


int main()
{
    // initialised variables
    int count = 0;
    char selector = 'q', yesNoAnswer = 'n';
    string name;
    string title;

    // asks user for file pathname
    cout << "Welcome to Tommy's Library Database." << endl;
    cout << "Please enter the name of the file: ";
    getline(cin, pathName);
    loadData();
    count = loadData();
    cout << count << " Records loaded successfully." << endl;
    // Switch case menu
    do {
        cout << endl << "Please enter a keyword that corresponds to the list of options: " << endl;
        cout << " Search by: (A)uthor, (T)itle, (S)how All, (Q)uit Program: ";
        cin >> selector;
        selector = toupper(selector);
        switch (selector)
        {
        case 'S':
            sortByTitle(count, title);
            if (count <= 0) {
                cout << " No counts found! " << endl;
            }
            else {
                showAll(count);
            }
            break;
        }
    }
    while (selector != 'q' && selector != 'Q');
    return 0;
}

int loadData()
{
    int count = 0;
    int i = 0;

    lib.open(pathName);
    ifstream lib(pathName);

    if (!lib)
    {
        cout << " Unable to open file path! " << endl;
        return -1;
    }
    while (!lib.eof())
    {
        getline(lib, books[count].title);
        getline(lib, books[count].author);
        count++;
    }
    return count;
}
// displays all book titles beside the author names
void showAll(int count)
{
    for (int i = 0; i < count; i++)
    {
        cout << books[i].title << " " << "(" << books[i].author << ")" << endl;
    }
}
// Sorts by book title.
void sortByTitle(int count, string title) {
    std::sort(books, books + count, [](const auto &lhs, const auto &rhs) {
        return lhs.title < rhs.title;
    });
}

In addition:

• You shouldn't read a stream with while (!lib.eof()) : Why is iostream::eof inside a loop condition (ie while (!stream.eof()) ) considered wrong?
• You can remove the first loadData()
• You can remove the second parameter of void sortByTitle(int count)
• You are shadowing global variables with local variables, eg global ifstream lib and local ifstream lib in int loadData()
• You can remove unused variables
• You should remove using namespace std; : Why is “using namespace std;” considered bad practice?
• You should avoid global variables
• You should replace endl by '\\n' if you don't need to flush in that moment. endl does more than a simple linebreak and usually it's not necessary.

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>

using std::cin;
using std::cout;
using std::ifstream;
using std::string;

// structure
struct Book {
    string title;
    string author;
};

const int ARRAY_SIZE = 1000;

// global variables
int loadData(string pathName, Book *books);
void showAll(Book *books, int count);
void sortByTitle(Book *books, int count);


int main()
{
    // initialised variables
    int count = 0;
    char selector = 'q';

    // asks user for file pathname
    cout << "Welcome to Tommy's Library Database.\n";
    cout << "Please enter the name of the file: ";
    string pathName;
    getline(cin, pathName);
    Book books[ARRAY_SIZE];
    count = loadData(pathName, books);
    cout << count << " Records loaded successfully.\n";
    // Switch case menu
    do {
        cout << "\nPlease enter a keyword that corresponds to the list of options: \n";
        cout << " Search by: (A)uthor, (T)itle, (S)how All, (Q)uit Program: ";
        cin >> selector;
        selector = toupper(selector);
        switch (selector)
        {
        case 'S':
            sortByTitle(books, count);
            if (count <= 0) {
                cout << " No counts found! \n";
            }
            else {
                showAll(books, count);
            }
            break;
        }
    }
    while (selector != 'q' && selector != 'Q');
    return 0;
}

int loadData(string pathName, Book *books)
{
    int count = 0;
    ifstream lib(pathName);

    if (!lib)
    {
        cout << " Unable to open file path! \n";
        return -1;
    }
    while (getline(lib, books[count].title))
    {
        getline(lib, books[count].author);
        count++;
    }
    return count;
}
// displays all book titles beside the author names
void showAll(Book *books, int count)
{
    for (int i = 0; i < count; i++)
    {
        cout << books[i].title << " " << "(" << books[i].author << ")\n";
    }
}
// Sorts by book title.
void sortByTitle(Book *books, int count) {
    std::sort(books, books + count, [](const auto &lhs, const auto &rhs) {
        return lhs.title < rhs.title;
    });
}