If any of the following conditions is satisfied, the behavior is undefined:

• [first, middle) or[middle, last) is not avalid range.

[edit]Parameters

[edit]Return value

The iterator to the element originally referenced by*first, i.e. thestd::distance(middle, last)th next iterator offirst.

[edit]Complexity

At moststd::distance(first, last) swaps.

[edit]Exceptions

The overload with a template parameter namedExecutionPolicy reports errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory,std::bad_alloc is thrown.

[edit]Possible implementation

See also the implementations inlibstdc++,libc++, andMSVC STL.

template<class ForwardIt>constexpr// since C++20ForwardIt rotate(ForwardIt first, ForwardIt middle, ForwardIt last){if(first== middle)return last; if(middle== last)return first;     ForwardIt write= first;    ForwardIt next_read= first;// read position for when “read” hits “last” for(ForwardIt read= middle; read!= last;++write,++read){if(write== next_read)            next_read= read;// track where “first” wentstd::iter_swap(write, read);} // rotate the remaining sequence into place    rotate(write, next_read, last);return write;}

[edit]Notes

std::rotate has better efficiency on common implementations ifForwardIt satisfiesLegacyBidirectionalIterator or (better)LegacyRandomAccessIterator.

Implementations (e.g.MSVC STL) may enable vectorization when the iterator type satisfiesLegacyContiguousIterator and swapping its value type calls neither non-trivial special member function norADL-foundswap.

[edit]Example

#include <algorithm>#include <iostream>#include <vector> auto print=[](constauto remark,constauto& v){std::cout<< remark;for(auto n: v)std::cout<< n<<' ';std::cout<<'\n';}; int main(){std::vector<int> v{2,4,2,0,5,10,7,3,7,1};    print("before sort:\t\t", v); // insertion sortfor(auto i= v.begin(); i!= v.end();++i)        std::rotate(std::upper_bound(v.begin(), i,*i), i, i+1);    print("after sort:\t\t", v); // simple rotation to the left    std::rotate(v.begin(), v.begin()+1, v.end());    print("simple rotate left:\t", v); // simple rotation to the right    std::rotate(v.rbegin(), v.rbegin()+1, v.rend());    print("simple rotate right:\t", v);}

before sort:2 4 2 0 5 10 7 3 7 1after sort:0 1 2 2 3 4 5 7 7 10simple rotate left:1 2 2 3 4 5 7 7 10 0simple rotate right:0 1 2 2 3 4 5 7 7 10

[edit]Defect reports

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

[edit]See also

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