为什么我可以将作为函数参数传递的字符串标记为字符串而不是使用getline检索的字

Question

我遇到的问题是我能够成功标记输入到我的函数parameters的字符串menucall，但是使用相同的方法我无法正确地标记从文件中获取的字符串getline我不明白为什么。两个字符串都被正确分成了令牌。所有由字符串参数构成的标记都会删除其前导空格，而由字符串书制作的标记上的所有前导空格都不会。

Book和Bookstore是我创建的类。此后有更多代码，但它取决于这两个字符串的标记化。我的函数调用如下所示：

menuCall("1, BookInput.txt", store);

我的输入文件中的第一行如下所示：

12345, Michael Main, Data Structures, 100.00

void menuCall(string parameters, Bookstore bookstore)
{
    ifstream in; 
    int i, o, option;
    int j = 0, p = 0;
    string optionToken, bookToken, book;
    string *sp, *so;
    Book newBook;
    sp = new string[5];
    so = new string[4];

    while (parameters != "")                                            //Check if the string is empty
    {
        i = parameters.find(",", 0);                                    //Find next comma in the string
        if (i > 0)                                                      //If a comma is found
        {
            optionToken = parameters.substr(0, i);                      //Substring ends at first comma
            parameters.erase(0, i + 1);                                 //Delete substring and comma from original string
            while (optionToken[0] == ' ')                               //Check for spaces at beginning of token
            {
                optionToken.erase(0, 1);                                //Delete spaces at beginning of token
            }
        }
        if (i < 0)                                                      //If no comma is found
        {
            optionToken = parameters;                                   //Substring ends at the end of the original string
            parameters.erase(0, i);                                     //Delete substring from original string
            while (optionToken[0] == ' ')                               //Check for spaces at beginning of token
            {
                optionToken.erase(0, 1);                                //Delete spaces at beginning of token
            }
        }
        sp[j] = optionToken;                                            //Token is added to dynamic array
        j++;                                                            //Keeps track of iterations
    }

    option = stoi(sp[0]);                                               //Change option number from string to usable int

    switch (option)                                                     //Switch to determine what menu option is to be performed
    {
    case(1):                                                            //Case 1
        in.open(sp[1]);                                                 //Open file from extracted token containing file name
        while (!in.eof())
        {
            getline(in, book);                                          //Get string containing book information from input file file
            while (book != "")                                          //Check if the string is empty
            {
                o = book.find(",", 0);                                  //Find the next comma in the string
                if (o > 0)                                              //If a comma is found
                {
                    bookToken = book.substr(0, o);                      //Substring ends at first comma
                    book.erase(0, o + 1);                               //Delete substring and comma from original string
                    while (bookToken[0] == ' ')                         //Check for spaces at beginning of token
                    {
                        bookToken.erase(0, 1);                          //Delete spaces at beginning of token
                    }
                }
                if (o < 0)                                              //If no comma is found
                {
                    bookToken = book;                                   //Substring ends at the end of the original string
                    book.erase(0, o);                                   //Delete substring from original string
                    while (bookToken[0] == ' ')                         //Check for spaces at beginning of token
                    {
                        bookToken.erase(0, 1);                          //Delete spaces at beginning of token
                    }
                }
                so[p] = bookToken;                                      //Token is added to dynamic array
                p++;                                                    //Keeps track of iterations
            }
        }
        break;