C++ interview questions and answers

I check has_value or use value_or before value().

A data race is concurrent conflicting access without sync — UB in C++.

Mutual exclusion around a critical section sharing state.

Threads wait until a predicate becomes true and get notified.

When one concrete type needs a completely different implementation than the primary template.

They accept a parameter pack of types or values.

Constructing an object in pre-allocated storage.

It provides a uniform interface over allocators with defaults.

noexcept tells the compiler the function will not throw.

Each entity should have essentially one definition across the program.

A non-owning view over contiguous elements with length.

Auto unpacking of pairs, tuples, and aggregates into named variables.

Many std::string implementations store short strings inside the object without heap.

Deleting a derived object through a base pointer needs a virtual destructor or you get UB.

Compile-time branching in templates so discarded branches need not be instantiable.

async may run deferred or on another thread depending on policy.

emplace constructs in place from arguments

Wrap fopen or OS handles in a class or unique_ptr with a custom deleter.

It does not own memory, so temporaries can dangle.

Curiously Recurring Template Pattern gives static polymorphism without virtual calls.