为什么我的一半没有打印出来？

我正在使用Getter函数从类中打印一个语句。我的代表语句的前1.5行没有打印。我尝试了冲洗流，还复制并粘贴了在if语句之外未打印的线条，并打印出来！我不知道发生了什么。这是功能：

// display all books out on loan
void displayBorrowed(vector<LibraryBook>& book)
{
    cout << "Books currently checked out: " << endl << endl;
    for(unsigned int i = 0; i < book.size(); i++)
    {
        //cout << "ID: " << book[i].getId_() << "  Title: " 
             //<< book[i].getTitle_() << endl << endl;
        if(book[i].getIsLoaned_() == true)
        { 
            std::cout.flush();
            cout << "ID: " << book[i].getId_() << "  Title: "
                 << book[i].getTitle_() << "  Author: " 
                 << book[i].getAuthorFirst_() << " " << book[i].getAuthorLast_()
                 << "  Year Published: " <<  book[i].getYearPubl_() << endl
                 << "Due Date: " << book[i].getDueMonth_() << "/" 
                 << book[i].getDueDay_() << "/" << book[i].getDueYear_()
                 << " Date Borrowed:  " << book[i].getBorrwdMonth_() << "/"
                 << book[i].getBorrwdDay_() << "/" << book[i].getBorrwdYear_()
                 << endl << "Checked out by: " << book[i].getBorrwFirst_()
                 << " " <<  book[i].getBorrwLast_() << endl << endl;
        }
    }
}

它显示了：

Books currently checked out:
  Author: Brendan Behan  Year Published: 1958
Due Date: 8/2/2017 Date Borrowed:  7/21/2017
Checked out by: Cassie Peterson

如果if语句中的行是从if语句中复制的，则它会正常显示：

ID：78620标题：Zhuan Falun

我尝试将IF语句更改为False以显示所有未借贷的书，除最后一本书外，它们都显示了相同的内容(第50本书最终显示了ID＃和标题。我完全亏损了。发生了什么？

应该看起来像这样：

ID: 78620  Title:  Zhuan Falun Author: Brendan Behan  Year Published: 1958
Due Date: 8/2/2017 Date Borrowed:  7/21/2017
Checked out by: Cassie Peterson

(尚未格式化显示(

我只是将其更改为此，其中我的每个元素在其自己的代表语句中都没有显示，并且没有显示！什么？？！(直到作者，我的意思是之前开始显示的地方。(

    for(unsigned int i = 0; i < book.size(); i++)
    {
        if(book[i].getIsLoaned_() == true)
        { 
            std::cout.flush();
            cout << "ID: " ;
            cout << book[i].getId_();
            cout << "  Title: ";
            cout <<  book[i].getTitle_();
            cout << "  Author: " 
                 << book[i].getAuthorFirst_() << " " << book[i].getAuthorLast_()
                 << "  Year Published: " <<  book[i].getYearPubl_() << endl
                 << "Due Date: " << book[i].getDueMonth_() << "/" 
                 << book[i].getDueDay_() << "/" << book[i].getDueYear_()
                 << " Date Borrowed:  " << book[i].getBorrwdMonth_() << "/"
                 << book[i].getBorrwdDay_() << "/" << book[i].getBorrwdYear_()
                 << endl << "Checked out by: " << book[i].getBorrwFirst_()
                 << " " <<  book[i].getBorrwLast_() << endl << endl;
        }
It prints when I put an endl at the end of each element:
        if(book[i].getIsLoaned_() == true)
        { 
            std::cout.flush();
            cout << "ID: " << endl;
            cout << book[i].getId_() << endl;
            cout << "  Title: " << endl;
            cout <<  book[i].getTitle_() << endl;
            cout << "  Author: "  << endl;
            cout << book[i].getAuthorFirst_() << " " << book[i].getAuthorLast_() << endl;
            cout << "  Year Published: " <<  book[i].getYearPubl_() << endl;
            cout << "Due Date: " << book[i].getDueMonth_() << "/"  << endl;
            cout << book[i].getDueDay_() << "/" << book[i].getDueYear_() << endl;
            cout << " Date Borrowed:  " << book[i].getBorrwdMonth_() << "/" << endl;
            cout << book[i].getBorrwdDay_() << "/" << book[i].getBorrwdYear_() << endl;
            cout << endl << "Checked out by: " << book[i].getBorrwFirst_() << endl;
            cout << " " <<  book[i].getBorrwLast_() << endl << endl;
        }

Books currently checked out:
ID:
47492
  Title:
 Borstal Boy
  Author:
Brendan Behan
  Year Published: 1958
Due Date: 8/
2/2017
 Date Borrowed:  7/
21/2017
Checked out by: Cassie
 Peterson