0 — Test 602

Correct Answer: A. map is O(log n) (a balanced tree, ordered); unordered_map is O(1) on average (a hash table)
Explanation: A common misconception is that map is a hash table. It is usually a red-black tree.

Correct Answer: D. If the vector reallocates, every iterator, pointer, and reference to its elements is invalidated
Explanation: Calling reserve() in advance prevents reallocation up to the reserved capacity.

Correct Answer: C. It cannot be copied, only moved (with std::move)
Explanation: shared_ptr uses reference counting and can be copied.

Correct Answer: D. Memory leak, because neither reference count reaches zero; one link should be a weak_ptr
Explanation: weak_ptr does not increase the reference count, which breaks the cycle. ALSO KNOW (related points): • What happens with auto s = "abc" + "def"; in C++? → Compilation error, because two const char pointers cannot be added • In what order are local objects a, b, and c destroyed, given they were constructed in that order? → c, b, a • Where should template function definitions normally be placed? → In the header file, because the compiler needs the full definition to instantiate templates • In C++11, how many times is the copy constructor called by return local_obj; inside a function? → Usually zero, because of return value optimization (RVO) or a move

Correct Answer: A. [=] captures variables by value; [&] captures them by reference
Explanation: A lambda that captures locals by reference and outlives them leaves dangling references.

Correct Answer: B. It cannot modify non-mutable data members of the object
Explanation: Members declared mutable can still be changed inside a const function.

Correct Answer: C. std::terminate() is called
Explanation: Since C++11, destructors are noexcept by default.

Correct Answer: C. 0, implicitly
Explanation: This special rule applies only to main. Other non-void functions have undefined behavior if they fall off the end.

Correct Answer: C. std::endl inserts a newline and flushes the stream; '\n' only inserts a newline
Explanation: Unnecessary flushing in loops can make output much slower.

Correct Answer: C. The newline left in the input buffer by >> is read by getline as an empty line
Explanation: Call cin.ignore() (or use std::ws) before calling getline.