std::shift_left,std::shift_right(3)

NAME
std::shift_left,std::shift_right - std::shift_left,std::shift_right

Synopsis
   Defined in header <algorithm>
   template< class ForwardIt >
   constexpr ForwardIt shift_left( ForwardIt first, ForwardIt last,
                        typename (1) (since C++20)
   std::iterator_traits<ForwardIt>::
                        difference_type n );
   template< class ExecutionPolicy, class ForwardIt >
   ForwardIt shift_left( ExecutionPolicy&& policy,
                        ForwardIt first, ForwardIt last, (2) (since C++20)
                        typename std::iterator_traits<ForwardIt>::
                        difference_type n );
   template< class ForwardIt >
   constexpr ForwardIt shift_right( ForwardIt first, ForwardIt last,
                        typename (3) (since C++20)
   std::iterator_traits<ForwardIt>::
                        difference_type n );
   template< class ExecutionPolicy, class ForwardIt >
   ForwardIt shift_right( ExecutionPolicy&& policy,
                        ForwardIt first, ForwardIt last, (4) (since C++20)
                        typename std::iterator_traits<ForwardIt>::
                        difference_type n );
   Shifts the elements in the range [first, last) by n positions.
   1) Shifts the elements towards the beginning of the range.
     * If n == 0 || n >= last - first, there are no effects.
     * Otherwise, for every integer i in [0, last - first - n), moves the element
       originally at position first + n + i to position first + i.
   The moves are performed in increasing order of i starting from 0.
   3) Shifts the elements towards the end of the range.
     * If n == 0 || n >= last - first, there are no effects.
     * Otherwise, for every integer i in [0, last - first - n), moves the element
       originally at position first + i to position first + n + i.
   If ForwardIt meets the LegacyBidirectionalIterator requirements, then the moves are
   performed in decreasing order of i starting from last - first - n - 1.
   2,4) Same as (1) and (3), respectively, but executed according to policy and the
   moves may be performed in any order.
   These overloads participate in overload resolution only if
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.
   Elements that are in the original range but not the new range are left in a valid
   but unspecified state.
   If any of the following conditions is satisfied, the behavior is undefined:
     * n >= 0 is not true.
     * The type of *first is not MoveAssignable.
     * For shift_right, ForwardIt is neither LegacyBidirectionalIterator nor
       ValueSwappable.

Parameters
   first - the beginning of the original range
   last - the end of the original range
   n - the number of positions to shift
   policy - the execution policy to use. See execution policy for details.

Type requirements
   -
   ForwardIt must meet the requirements of LegacyForwardIterator.

Return value
   1,2) The end of the resulting range.
     * If n is less than std::distance(first, last), returns an iterator equal to
       std::next(first, (std::distance(first, last) - n)).
     * Otherwise, returns first.
   3,4) The beginning of the resulting range.
     * If n is less than std::distance(first, last), returns an iterator equal to
       std::next(first, n).
     * Otherwise, returns last.

Complexity
   1,2) At most std::distance(first, last) - n assignments.
   3,4) At most std::distance(first, last) - n assignment or swaps.

Exceptions
   The overloads with a template parameter named ExecutionPolicy report errors as
   follows:
     * If execution of a function invoked as part of the algorithm throws an exception
       and ExecutionPolicy is one of the standard policies, std::terminate is called.
       For any other ExecutionPolicy, the behavior is implementation-defined.
     * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Notes
   Feature-test macro Value Std Feature
   __cpp_lib_shift 201806L (C++20) std::shift_left and std::shift_right

Example
// Run this code
 #include <algorithm>
 #include <iostream>
 #include <string>
 #include <type_traits>
 #include <vector>
 struct S
 {
     int value{0};
     bool specified_state{true};
     S(int v = 0) : value{v} {}
     S(S const& rhs) = default;
     S(S&& rhs) { *this = std::move(rhs); }
     S& operator=(S const& rhs) = default;
     S& operator=(S&& rhs)
     {
         if (this != &rhs)
         {
             value = rhs.value;
             specified_state = rhs.specified_state;
             rhs.specified_state = false;
         }
         return *this;
     }
 };
 template<typename T>
 std::ostream& operator<<(std::ostream& os, std::vector<T> const& v)
 {
     for (const auto& s : v)
     {
         if constexpr (std::is_same_v<T, S>)
             s.specified_state ? os << s.value << ' ' : os << ". ";
         else if constexpr (std::is_same_v<T, std::string>)
             os << (s.empty() ? "." : s) << ' ';
         else
             os << s << ' ';
     }
     return os;
 }
 int main()
 {
     std::cout << std::left;
     std::vector<S> a{1, 2, 3, 4, 5, 6, 7};
     std::vector<int> b{1, 2, 3, 4, 5, 6, 7};
     std::vector<std::string> c{"α", "β", "γ", "δ", "ε", "ζ", "η"};
     std::cout << "vector<S> \tvector<int> \tvector<string>\n";
     std::cout << a << " " << b << " " << c << '\n';
     std::shift_left(begin(a), end(a), 3);
     std::shift_left(begin(b), end(b), 3);
     std::shift_left(begin(c), end(c), 3);
     std::cout << a << " " << b << " " << c << '\n';
     std::shift_right(begin(a), end(a), 2);
     std::shift_right(begin(b), end(b), 2);
     std::shift_right(begin(c), end(c), 2);
     std::cout << a << " " << b << " " << c << '\n';
     std::shift_left(begin(a), end(a), 8); // has no effect: n >= last - first
     std::shift_left(begin(b), end(b), 8); // ditto
     std::shift_left(begin(c), end(c), 8); // ditto
     std::cout << a << " " << b << " " << c << '\n';
 // std::shift_left(begin(a), end(a), -3); // UB, e.g. segfault
 }

Possible output:
 vector<S> vector<int> vector<string>
 1 2 3 4 5 6 7 1 2 3 4 5 6 7 α β γ δ ε ζ η
 4 5 6 7 . . . 4 5 6 7 5 6 7 δ ε ζ η . . .
 . . 4 5 6 7 . 4 5 4 5 6 7 5 . . δ ε ζ η .
 . . 4 5 6 7 . 4 5 4 5 6 7 5 . . δ ε ζ η .

See also
   move moves a range of elements to a new location
   (C++11) (function template)
   move_backward moves a range of elements to a new location in backwards order
   (C++11) (function template)
   rotate rotates the order of elements in a range
                       (function template)
   ranges::shift_left shifts elements in a range
   ranges::shift_right (niebloid)
   (C++23)