Modern C++ MCQs - Smart Pointers, Move Semantics and Lambdas (Set 4)

Q1. Which statement about std::unique_ptr is true?

a) It can be freely copied

b) It can be moved but not copied

c) It keeps a reference count

d) It never frees its memory

Q2. What is printed?

auto a = make_shared<int>(5);
auto b = a;
{
  auto c = a;
}
cout << a.use_count();

a) 1

b) 2

c) 3

d) 0

Q3. What is the main purpose of std::weak_ptr?

a) To make shared_ptr thread-safe

b) To observe a shared object without owning it, which breaks reference cycles

c) To replace raw pointers in arrays

d) To allocate memory faster

Q4. What does std::move actually do?

a) Moves the object's bytes to a new address

b) Casts its argument to an rvalue reference so that a move constructor or move assignment can be chosen

c) Deletes the original object

d) Copies the object and then clears it

Q5. After string a = "hi"; string b = std::move(a); what is guaranteed about a?

a) a still equals "hi"

b) a is destroyed and cannot be used

c) a is in a valid but unspecified state

d) Accessing a is a compile error

Q6. What type is deduced for x in auto x = 5u; ?

a) int

b) unsigned int

c) long

d) size_t

Q7. What is printed?

int x = 1;
auto f = [x]() { return x; };
x = 10;
cout << f();

a) 1

b) 10

c) 0

d) Compilation error

Q8. What is printed?

int x = 1;
auto f = [&x]() { return x; };
x = 10;
cout << f();

a) 1

b) 10

c) 0

d) Compilation error

Q9. Which declaration declares an rvalue reference to int?

a) int &r

b) int &&r

c) int *&r

d) const int &r

Q10. Why is nullptr preferred over NULL in modern C++?

a) It is faster at run time

b) It has its own type (std::nullptr_t), so it never gets confused with an int in overload resolution

c) NULL was removed from C++

d) nullptr can be dereferenced safely

Q11. What is printed?

vector<int> v = {1, 2, 3};
for (auto &x : v) x *= 2;
int s = 0;
for (int x : v) s += x;
cout << s;

a) 6

b) 12

c) 3

d) 0

Q12. What does constexpr on a function mean?

a) It must be inlined

b) It can be evaluated at compile time when called with constant arguments

c) It can never be called at run time

d) It runs only once

Q13. How does emplace_back differ from push_back?

a) It inserts at the front

b) It constructs the element directly inside the container from the given arguments

c) It does not allocate memory

d) It sorts the vector after inserting

Q14. Which of these is NOT one of the five special member functions in the Rule of Five?

a) Move constructor

b) Copy assignment operator

c) Default constructor

d) Destructor

Q15. Why is it important to mark a move constructor noexcept?

a) It makes the code compile faster

b) std::vector will only move elements during reallocation if the move constructor is noexcept; otherwise it copies them

c) noexcept is required for all constructors

d) It prevents the object from being copied