std::ranges::views::drop, std::ranges::drop_view - cppreference.com (original) (raw)

1. A range adaptor consisting of elements of the underlying sequence, skipping the first N elements.

2. RangeAdaptorObject. Given T is std::remove_cvref_t<decltype((e))> and D is ranges::range_difference_t<decltype((e))>), the expression views::drop(e, f) is expression-equivalent to:

• ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the evaluations of e and f are indeterminately sequenced;

• otherwise, T(ranges::begin(e) + inc, ranges::end(e),
  /*to-unsigned-like*/(ranges::distance(e) - inc)), if T is a specialization of ranges::subrange that models both random_access_range and sized_range, and T needs to store the size (see ranges::subrange::subrange() for details), where inc is std::min<D>(ranges::distance(e), f);

• otherwise, U(ranges::begin(e) + inc, ranges::end(e)), if T is a specialization of std::span, std::basic_string_view, ranges::iota_view, or ranges::subrange that models both random_access_range and sized_range, where U is

• std::span<typename T::element_type>, if T is a specialization of std::span;

• T otherwise;

• otherwise, drop_view(e, f).

In all cases, decltype((f)) must model std::convertible_to<D>.

drop_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, common_range, and sized_range when the underlying view V models respective concepts.

Contents

• 1 Data members
• 2 Member functions
  • 2.1 Inherited from std::ranges::view_interface
• 3 Deduction guides
• 4 Helper templates
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Data members

[edit] Member functions

[edit] Deduction guides

[edit] Helper templates

This specialization of ranges::enable_borrowed_range makes drop_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Example

#include #include #include   int main() { const auto nums = {1, 2, 3, 4, 5, 6, 7};   std::cout << "drop " << 2 << ": "; for (int i : std::ranges::drop_view{nums, 2}) std::cout << i << ' '; std::cout << '\n';   std::cout << "drop " << 3 << ": "; for (int i : nums | std::views::drop(3)) std::cout << i << ' '; std::cout << '\n';   std::cout << "drop " << 4 << ": "; for (int i : std::views::iota(1, 8) | std::views::drop(4)) std::cout << i << ' '; std::cout << '\n';   // Note that dropping more than the number of elements is OK: for (int dp : {5, 6, 7, 890, 100500}) { std::cout << "drop " << dp << ": "; for (int i : std::views::iota(1, 8) | std::views::drop(dp)) std::cout << i << ' '; std::cout << '\n'; } }

Output:

drop 2: 3 4 5 6 7 drop 3: 4 5 6 7 drop 4: 5 6 7 drop 5: 6 7 drop 6: 7 drop 7: drop 890: drop 100500:

[edit] Defect reports

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

[edit] See also