C++17 vs C++20 – Key Feature Differences

C++17 vs C++20: Top 5 Modern Features Compared (with Examples)

Are you transitioning from C++17 to C++20 or working on mixed codebases? Here are the 5 most important feature differences you need to know, with simple examples:

1. Structured Bindings (C++17) vs Designated Initializers (C++20)

std::pair<int, std::string> p = {1, "apple"};
auto [id, name] = p;

struct Fruit { int id; std::string name; };
Fruit f = {.name = "apple", .id = 1};

2. if constexpr (C++17) vs Concepts (C++20)

template<typename T>
void print_type(T value) {
    if constexpr (std::is_integral_v<T>) {
        std::cout << "Integer: " << value << "\n";
    } else {
        std::cout << "Other: " << value << "\n";
    }
}

template<std::integral T>
void print_integral(T value) {
    std::cout << "Integer: " << value << "\n";
}

3. std::optional vs std::span

std::optional<int> maybe_id;
if (!maybe_id) maybe_id = 42;

void print_all(std::span<int> data) {
    for (int x : data) std::cout << x << " ";
}
std::vector<int> v = {1, 2, 3};
print_all(v);

4. Inline Variables vs consteval

inline constexpr int MaxCount = 100;

consteval int square(int x) { return x * x; }
int x = square(5); // Compile time

5. Ranges, Coroutines, and the Spaceship Operator

• <=> for automatic comparison
• ranges::views::filter for cleaner pipelines
• co_yield, co_return enable coroutine usage

📥 Download the free C++17 Cheatsheet

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