C ++：将文本文件解析并读入数组

Question

I was hoping that I could find some help here. I have an assignment due next week that involves reading a bunch of data from a txt file into an array, and then printing out the results. The data is in the following format:

"Macbeth","William Shakespeare","41.04","161","23","978-88-5985-004-5"

"A Christmas Carol","Charles Dickens","98.74","167","547","978-26-2885-780-7". .

.

.

Each row has six pieces of information that I need to store for later use. I'm supposed write code that counts the number of lines of text we have in order to create a dynamic array of the correct size. I've got that covered. I've got 39 lines entries. Then I'm supposed to create a function that reads the txt file and saves all of that data to the corresponding object in the array that I created.

I don't know what methods to use, and I've been looking around for tutorials and explanations for a few days. I have extremely limited experience with files and parsing, so excuse me if I'm a little inexperienced. Here's my code so far:

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

using namespace std;


class Author
{
    public:

private:
    string fname, lname;

};

class Book
{
    friend ofstream& operator<<(ofstream&, Book);

        public:
        Book();

    private:
        string bookName;
        Author author;
        double price;
        int qtyOnHand;
        int qtySold;
        double revenue;
        string ISBN;

};

Book :: Book()
{

}

int getLineNumber(ifstream &);
void parseData(ifstream &, Book []);


//void sortBookList(Book[], int, int);


int main()
{
    int numberOfBooks;

    //open the file from which to read the data
    ifstream myFile;
    myFile.open("Book List.txt");
    //function to find out how many objects to create
    numberOfBooks = getLineNumber(myFile);

    //create an array with that many objects
    Book *bptr;
    bptr = new Book[numberOfBooks];
    //function to read information from file into array of objects
    parseData(myFile, bptr);

    //loop to call sorting function and output function based on 4 different criteria

    //close the file explicitly
    return 0;
}

int getLineNumber(ifstream &myFile)
{
    int counter = 0;
    string myString;


    while(!myFile.eof())
    {
        getline(myFile, myString);
        counter++;
    }

    myFile.close();

    counter --;
    return counter;
}

void parseData(ifstream &myFile, Book bookPtr[])
{

}

So, to summarize my issues, I don't understand how to parse data from the text file into my array. A very big thank you in advance to anyone that could help! Cheers.

EDIT: I've tried fooling around with the code, and I think I made a step in the right direction, but I'm still a little lost. Here's what I have for the parseData function.

void parseData(ifstream &myFile, Book bookPtr[])
{

    string dummyLine;

    string word, line;
    myFile.open("Book List.txt");
    getline(myFile, dummyLine);
    string data[6];

    while(!myFile.eof())
    {
        getline(myFile, line, '\n');

        for (size_t i = 0; i < line.size(); ++i)
        {
            char c = line[i];

            if(c == ',' || c == '\n')
            {
                if(!word.empty())
                {
                    data[i] = word;
                    word.clear();
                }
            }
            else
            {
                word += c;
            }


        }
        if(!word.empty())
        {
            //cout << word << endl;
        }
    }




}

Answer 1

Maybe you just need to know how to do something with each character in a string?

Here's some code that goes through each character of a string building up words, then prints them individually. You'll notice that string has the same interface as vector ( str[i] , str.push_back(char) , str.size() , etc.).

// You'll need to include <iostream> and <string>

std::string example = "This is an example string";
std::string word;

// Notice how you can loop through a string just like a vector<char>
for(size_t i = 0; i < example.size(); ++i) {
    char c = example[i];

    // When we see whitespace, print the current word and clear it
    if(c == ' ' || c == '\t' || c == '\n') {
        // Don't print anything if we don't have a word
        if(!word.empty()) {
            std::cout << word << std::endl;
            word.clear();
        }
    } else {
        // Append the current character to the end of the string
        word += c; // or word.push_back(c)
    }
}
// In case the line doesn't end with whitespace
if(!word.empty()) {
    std::cout << word << std::endl;
}

The std::basic_string (alias for std::string ) reference is probably useful.

Answer 2

You can use a vector data structure to hold the book class. vector records;

Answer 3

(I highly recommend to use a vector (or a list) for that because it will avoid the double reading of the file because you wouldn't need to know the number of line at all.)

To parse a line that has a fixed number of field, it easy in principle:

int counter = 0;
string myString;


while(!myFile.eof())
{
    getline(myFile, myString);
    counter++;
}
counter --;

//Clear the error state flag
myFile.clear()

//Return to the beginning of the file:
myFile.seekg(ios_base::beg);


const int fieldCount = 5;
string field[fieldCount ];


string buffer= "";
char c = '\0';
for( int i = 0; i < counter; ++i ) {
    for( int j = 0; j < fieldCount; ++j ) {
        myFile.ignore(); //Ignore the first '"'
        //Read each character up to the second '"'
        while( myFile.good() && (c = myfile.get()) != '"' ) {
            buffer += c;
        }
        field[j] = buffer;
        buffer = "";
        if( j != fieldCount - 1 ) {
            myFile.ignore(); //Ignore the first ','
        }
    }

    //Use the fields here.

}

I didn't test this code, I know there a lack of error-testing, but It shows a way to do it.