const string &book)

{

vector<matches> ret; //初始化为空vector

// 对每家书店，查找给定书籍匹配的记录范围

for (auto it = files.cbegin; it != files.cend(); ++it)

{

// 查找具有相同ISBN的Sales_data范围，found是一个迭代器pair

auto found = equal_range(it->cbegin(), it->cend(), book, compareIsbn);

if (found.first != found.second) // 此书店销售了给定书籍

// 记住此书店的索引及匹配的范围

ret.push_back(make_tuple(it - files.cbegin(), found.first, found.second));

}

return ret; //如果未找到匹配记录，ret为空

const vector<vector<Sales_data> > &files){

string s; //要查找的书

while (in >> s){

auto trans = findBook(files, s);

if (trans.empty()){

cout << s << " not found in any stores" << endl;

continue; // 获得下一本要查找的书

}

for (const auto &store : trans) // 对每家销售了给定书籍的书店

// get<n>返回store中tuple的指定的成员

os << "store " << get<0>(store) << " sales: "

<< accumulate(get<1>(store), get<2>(store), Sales_data(s))

<< endl;

}