std::ranges::transform_view<V,F>::transform_view - cppreference.com (original) (raw)

Constructs a transform_view.

1. Default constructor. Value-initializes the underlying view _[base](../transform%5Fview.html#base "cpp/ranges/transform view")_ and the transformation function _[fun](../transform%5Fview.html#fun "cpp/ranges/transform view")_.

2. Move constructs the underlying view _[base](../transform%5Fview.html#base "cpp/ranges/transform view")_ from base and the transformation function _[fun](../transform%5Fview.html#fun "cpp/ranges/transform view")_ from fun.

[edit] Parameters

[edit] Example

Demonstrates π approximation using serial expansion of arc tangent of 1: atan(1) = π/4 ≈ 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...

#include #include #include #include #include #include   int main() { std::cout << std::setprecision(15) << std::fixed; auto atan1term{std::ranges::views::transform ( [](int n) { return ((n % 2) ? -1 : 1) * 1.0 / (2 * n + 1); } )}; for (const int iterations : {1, 2, 3, 4, 5, 10, 100, 1000, 1'000'000}) { auto seq{std::ranges::views::iota(0, iterations) bitor atan1term}; const double accum{*std::ranges::fold_left_first(seq, std::plus{})}; std::cout << "π ≈ " << 4 * accum << " (iterations: " << iterations << ")\n"; } std::cout << "π ≈ " << std:🔢:pi << " (std:🔢:pi)\n"; }

Possible output:

π ≈ 4.000000000000000 (iterations: 1) π ≈ 2.666666666666667 (iterations: 2) π ≈ 3.466666666666667 (iterations: 3) π ≈ 2.895238095238096 (iterations: 4) π ≈ 3.339682539682540 (iterations: 5) π ≈ 3.041839618929403 (iterations: 10) π ≈ 3.131592903558554 (iterations: 100) π ≈ 3.140592653839794 (iterations: 1000) π ≈ 3.141591653589774 (iterations: 1000000) π ≈ 3.141592653589793 (std:🔢:pi)

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.