C++ vector iterator std::ref(vec)

void Util::getStructVector(vector<BookStruct> &vec, int len)
{
    for (int i = 0; i < len; i++)
    {
        BookStruct bs;
        bs.BookIndex = i;
        bs.BookId = (unsigned long long)i * i * i * i * i * i;
        bs.BookName = (char *)malloc(40);
        bs.BookTitle = (char *)malloc(40);
        strcpy(bs.BookName, getUuid27());
        strcpy(bs.BookTitle, getUuid27());
        vec.push_back(bs);
    }
}


char *Util::getUuid27()
{
    uuid_t newUUID;
    uuid_generate(newUUID);
    uuid_unparse(newUUID, Util::uuidValue);
    return Util::uuidValue;
}


void Util::printStructVector32(vector<BookStruct> &vec)
{
    vector<BookStruct>::iterator itr = vec.begin();
    while (itr != vec.end())
    {
        cout << fixed
             << "Index=" << itr->BookIndex << ",Id=" << itr->BookId << ",Name="
             << itr->BookName << ",Title=" << itr->BookTitle << endl;
        free(itr->BookName);
        free(itr->BookTitle);
        itr++;
    }
}

void Util::structVector33(int len)
{
    vector<BookStruct> vec;
    getStructVector(std::ref(vec), len);
    printStructVector32(std::ref(vec));
    cout << "Finished in void Util::structVector33(int len) and now is " << getTimeNow() << endl;
}

g++ -g -std=c++2a -I. *.cpp ./Model/*.cpp -o h1 -luuid -lpthread

time ./h1 10000