// using C++11 range-based for loop
BarcodeQuery query(42, dataset);
for (const BamRecord& r : query) {
    assert(r.HasBarcodes());
    assert(r.BarcodeForward() == 42 || r.barcodeReverse() == 42);
}

// OR

// using iterators directly
BarcodeQuery query(42, dataset);
auto iter = query.cbegin();
auto end  = query.cend();
for (; iter != end; ++iter) {
    assert(iter->HasBarcodes());
    assert(iter->BarcodeForward() == 42 || iter->barcodeReverse() == 42);
}