用字符串和整數逐行讀取文件

Question

我正在嘗試從以下文件中讀取信息：

The Firm
Dell
512
Fundamentals of Computer Graphics
A K Peters, Ltd.
662
The C++ Programming Language
Addison-Wesley Professional
911
Northwest Airlines
Plymouth Toy & Book
96
Lonely Planet: Europe on a Shoestring
Lonely Planet Publications
1324
…

該文件列出了書籍，第一行是書名，第二行是出版商，第三行是頁數，重復五本書。 我正在嘗試讀取信息，並將其存儲到Library類中的向量中。

class book

{


public:

    book();


    book(string t, string p, int num);


    string getTitle();
    string getPublisher();
    int getPageNum();


    void setTitle(string t);
    void setPublisher(string p);
    void setPageNum(int num);


    string title;
    string publisher;
    int num_of_pages;

};



  class library
    {
    public:
        vector<book> collection;

        bool contains(string title);

        void addBook(book b);

        void readFile(string fileName);
    }

這是readFile函數：

   void library::readFile(string fileName)
    {
        ifstream infile;
        infile.open(fileName.c_str());
        if (infile.fail())
        {
            cout<<"Error opening file."<<endl<<endl;
            exit(1);
        }

       book addition;
string line;

while (!infile.eof())
{
    getline(infile, addition.title);
    getline(infile, addition.publisher);
    getline(infile, line);
    addition.num_of_pages=atoi(line.c_str());
    collection.push_back(addition);  
}


        collection.push_back(addition);


    }

最后一個問題：輸出無法正常工作。 文件中的所有內容均列在標題下。

ostream &operator <<(ostream& out, const book& b1)
{
    out<<"TITLE: "<<b1.title<<endl;
    out<<"PUBLISHER: "<<b1.publisher<<endl;
    out<<"NUMBER OF PAGES: "<<b1.num_of_pages<<endl;

    return out;
}

主要代碼：

int i;
                for (i=0; i<book_library.collection.size(); i++)
                {
                    cout<<book_library.collection[i]<<endl;
                }

輸出：

TITLE: The Firm
Dell
512
Fundamentals of Computer Graphics
A K Peters, Ltd.
662
The C++ Programming Language
Addison-Wesley Professional
911
Northwest Airlines
Plymouth Toy & Book
96
Lonely Planet: Europe on a Shoestring
Lonely Planet Publications
1324
\311
PUBLISHER: 
NUMBER OF PAGES: 0

Answer 1

一種簡化可能是，因為getline返回一個istream ，以便在while條件下直接對其進行測試：

while (getline(infile, addition.title)) {
    getline(infile, addition.publisher);
    getline(infile, line);
    addition.num_of_pages = atoi(line.c_str()); // string -> int
    collection.push_back(addition);  // you should push_back in the while loop
}

Answer 2

您可以為您的book類定義一個提取運算符以將內容封裝起來，也可以使用標准的內置提取運算符（>>）來保存臨時變量和轉換：

std::ifstream & operator>>(std::ifstream & str, book & b)
{
    str >> b.title >> b.publisher >> b.num_of_pages;
    return str;
}

std::ifstream infile;
book addition;
std::vector<book> collection;
while ( infile >> addition)
{
    collection.push_back(addition);
}