Therange concept defines the requirements of a type that allows iteration over its elements by providing an iterator and sentinel that denote the elements of the range.

[edit]Semantic requirements

Given an expressionE such thatdecltype((E)) isT,T modelsrange only if

• [ranges::begin(E), ranges::end(E)) denotes arange, and
• bothranges::begin(E) andranges::end(E) are amortized constant time and do not alter the value ofE in a manner observable toequality-preserving expressions, and
• if the type ofranges::begin(E) modelsforward_iterator,ranges::begin(E) isequality-preserving (in other words, forward iterators support multi-pass algorithms).

[edit]Notes

A typicalrange class only needs to provide two functions:

1. A member functionbegin() whose return type modelsinput_or_output_iterator.
2. A member functionend() whose return type modelssentinel_for<It>, whereIt is the return type ofbegin().

Alternatively, they can be non-member functions, to be found byargument-dependent lookup.

[edit]Example

#include <ranges> // A minimum rangestruct SimpleRange{int* begin();int* end();};static_assert(std::ranges::range<SimpleRange>); // Not a range: no begin/endstruct NotRange{int t{};};static_assert(!std::ranges::range<NotRange>); // Not a range: begin does not return an input_or_output_iteratorstruct NotRange2{void* begin();int* end();};static_assert(!std::ranges::range<NotRange2>); int main(){}

[edit]Defect reports

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

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