C++ FileIO 读取和写入对象变量

Question

我正在尝试制作一个小型图书馆系统，用户可以在其中添加新书的详细信息（名称、作者和价格）。当实现 FileIO 系统以使用 getline 函数从文件中读取每本书的详细信息时，当我尝试将变量存储在临时变量中时，将它们分开变得更加困难。

例如：

"No Is a four letter word,Chris Jericho,17.67,"

"Harry Potter,JK Rowling,23.98,"

PS:有没有比添加逗号更好的解决方案？

我尝试添加一个“,”字符来分隔我的每个字符串，但我需要一个更好、更高效的解决方案来与 getLine 函数一起使用。

int main(){
vector<Book> library;
//----Loading File Data_START
string line;
int nbArg=0;

string tempName, tempAuthor, tempPrice;


ifstream myfileL("List.txt");
if (myfileL.is_open())
{
    while (getline(myfileL, line))
    {
        tempPrice=tempAuthor = tempName = "";
        for (int j = 0; j < line.size(); j++){

            if (line.at(j) == ','){
                nbArg++;


                }
            else{
                switch (nbArg){
                case 0:
                    tempName += (line.at(j));
                    break;
                case 1:
                    tempPrice += (line.at(j));
                    break;
                case 2:
                    tempAuthor += (line.at(j));

                    break;

            }
            }
        }

        cout << tempName << endl << tempAuthor << endl << tempPrice << endl;
        cout << "End of Line"<< endl;
        nbArg = 0;
    }
    cout << "---------------------------" << endl;
    myfileL.close();
}

else cout << "Unable to open file";

//----Loading File Data_END
char inputKey = 's';
cout << "-----------------WELCOME----------------" << endl;
while (inputKey != 'q')
{
    cout << "---------------------------------------" << endl;
    cout << "Click \"1\" to add a book to your library" << endl;
    cout << "Click \"2\" to show how the number of books your possess" << endl;
    cout << "Click \"3\" to show details about your books" << endl;
    cout << "Click \"q\" to quit" << endl;
    cin >> inputKey;

    switch (inputKey)
    {
    case '1':
        addElem(library);
        break;

    case '2':
        cout << "You now own " << libSize(library) << " books !" << endl;
        break;

    case '3':
        showDetails(library);
        break;

    case 'q':
        cout << "GOODBYE!" << endl;
        Sleep(2000);
        break;
    }
}

return 0;

}

Answer 1

使用可以包含结构的专用文件格式（例如json、xml）。这将避免很多很多问题。

如果不能，则添加一个分隔符（就像您所做的那样），但选择一个在实际字符串中出现的机会最少的字符。所以例如行尾（每个变量都会在它自己的行上）或 \0 或 \t.

Answer 2

这里有一个顺利加载库的解决方案。您可以让 BookList.txt 文件在名称、作者和价格之间用 TABs \t 分隔，而不是用逗号 , 分隔，然后使用 getline() 分隔TAB 如下例所示。

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <vector>
using namespace std;

const char TAB = '\t';

struct StructBook {
    string Name, Author;
    double Price;
};

vector<StructBook> Library;

void GetBookDetails(string LineBookDetails, StructBook & Book) {
    string string_Price;
    stringstream StringStreamBookDetails(LineBookDetails);
    getline(StringStreamBookDetails, Book.Name, TAB);
    getline(StringStreamBookDetails, Book.Author, TAB);
    getline(StringStreamBookDetails, string_Price, TAB);
    stringstream(string_Price) >> Book.Price;
}

bool LoadLibrary() {
    ifstream FileBookList("BookList.txt");
    if(FileBookList.is_open()) {
        string LineBookDetails;
        StructBook Book;

        while(getline(FileBookList, LineBookDetails)) {
            GetBookDetails(LineBookDetails, Book);
            Library.push_back(Book);
            cout << Book.Name << ", " << Book.Author << ", " << Book.Price << endl;
        }

        FileBookList.close();
        return true;
    } else {
        return false;
    }
}

int main(){
    if(!LoadLibrary())
        cout << "Error: Unable to load library";

    //Rest of your program goes here

    return 0;
}

您的 BookList.txt 应如下所示：

No Is a four letter word    Chris Jericho   17.67
Harry Potter    JK Rowling  23.98

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