E2 · Milestone Exam II — The Latency Lab

Milestone Exam II

12 questions · pass at 75%

Q01

std::move performs:

AA deep copyBA cast to rvalue reference, enabling a moveCA freeDA shallow copy

Whystd::move is only a cast; the move constructor/assignment does the actual stealing.

Q02

You define a destructor with delete[] but not a copy constructor. Copying an instance causes:

AA leakBA double free (two objects delete[] the same buffer)CA compile errorDNothing

WhyDefault shallow copy shares the pointer; both destructors free it. Rule of Five.

Q03

The Rule of Zero says:

AWrite all five special membersBUse RAII members so the compiler-generated special members are correct; write noneCNever allocateDAvoid destructors

WhyHold vector/unique_ptr members and let the defaults do copy/move/destroy correctly.

Q04

unique_ptr is move-only because:

ACopying is slowBIt models sole ownership; a copy would create two ownersCIt has a bugDThe standard forbids copying pointers

WhyExclusive ownership can't be duplicated; it can only transfer via move.

Q05

A reference cycle between two shared_ptrs results in:

AA double freeBA memory leakCA dangling pointerDCorrect cleanup

WhyCounts never hit zero; break the cycle with weak_ptr.

Q06

Which container gives O(1) average key lookup with no ordering?

AmapBunordered_mapCvectorDlist

Whyunordered_map is a hash table, O(1) average.

Q07

A vector reallocation invalidates:

ANothingBOnly the first iteratorCAll iterators, pointers, and references into itDOnly iterators after the insertion point

WhyGrowth moves the whole buffer, invalidating everything pointing into it.

Q08

Erasing one element from a std::map invalidates:

AAll iteratorsBOnly the iterator to the erased elementCIterators after itDNothing

WhyNode-based containers invalidate only the erased node's iterator.

Q09

The order book uses std::map for each side because:

AMaps hash fasterBThe best price is begin() of a sorted map, O(1) to readCMaps use less memoryDunordered_map can't hold prices

WhyMatching constantly needs the best price; a sorted map exposes it at begin().

Q10

Ranges in the STL are:

AClosed [begin, end]BHalf-open [begin, end)COpen (begin, end)DReversed

WhyHalf-open: begin included, end excluded. end() is a non-dereferenceable sentinel.

Q11

std::lower_bound requires the range to be ___ and runs in ___:

Aunsorted; O(n)Bsorted; O(log n)Csorted; O(1)Dunsorted; O(log n)

WhyBinary search needs a sorted range; it is O(log n) and returns the first element >= value.

Q12

A lambda that captures by reference and outlives the captured variable:

AIs fineBHolds a dangling reference — undefined behaviorCCopies the variableDFails to compile

WhySame lifetime bug as any dangling reference, now hidden in a callable. Capture by value if it may outlive the scope.

Memory · Moves · The STL

Before you start

Milestone Exam II