CPP Modern C++ Features (C++17/20) 5

Question 1

What does the C++20 three-way comparison operator `<=>` (spaceship operator) return when comparing two ints?

Accepted Answer

std::strong_ordering

Answer

Comparing ints with <=> produces std::strong_ordering because integers have a total order with no equivalent-but-unequal values.

Question 2

Which C++20 feature allows `Point p = {.x = 1, .y = 2};` initialization syntax?

Accepted Answer

Designated initializers

Answer

C++20 designated initializers let you name aggregate members by their field names in initialization, matching C99's syntax.

Question 3

How does `consteval` differ from `constexpr` in C++20?

Accepted Answer

consteval requires evaluation at compile time; constexpr permits runtime evaluation

Answer

A consteval function (immediate function) must be called in a constant expression context; it cannot be invoked at runtime unlike constexpr.

Question 4

What does `std::format("{:>10}", "hi")` produce in C++20?

Accepted Answer

"        hi" (right-aligned in a field of width 10)

Answer

> in the format spec means right-align; the string is padded with spaces on the left to fill a width-10 field.

Question 5

In C++20, `std::jthread` differs from `std::thread` primarily because:

Accepted Answer

It automatically joins on destruction and supports cooperative cancellation via stop_token

Answer

std::jthread's destructor calls request_stop() then join(), avoiding the terminate() that std::thread calls if destroyed while joinable.

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