std::inplace_merge
Defined in header <algorithm>


template< class BidirIt > void inplace_merge( BidirIt first, BidirIt middle, BidirIt last ); 
(1)  
template< class ExecutionPolicy, class BidirIt > void inplace_merge( ExecutionPolicy&& policy, BidirIt first, BidirIt middle, BidirIt last ); 
(2)  (since C++17) 
template< class BidirIt, class Compare> void inplace_merge( BidirIt first, BidirIt middle, BidirIt last, Compare comp ); 
(3)  
template< class ExecutionPolicy, class BidirIt, class Compare> void inplace_merge( ExecutionPolicy&& policy, BidirIt first, BidirIt middle, BidirIt last, Compare comp ); 
(4)  (since C++17) 
Merges two consecutive sorted ranges [first, middle)
and [middle, last)
into one sorted range [first, last)
. For equivalent elements in the original two ranges, the elements from the first range (preserving their original order) precede the elements from the second range (preserving their original order).
operator<
and the ranges must be sorted with respect to the same.comp
and the ranges must be sorted with respect to the same.policy
. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is trueContents 
[edit] Parameters
first    the beginning of the first sorted range 
middle    the end of the first sorted range and the beginning of the second 
last    the end of the second sorted range 
policy    the execution policy to use. See execution policy for details. 
comp    comparison function object (i.e. an object that satisfies the requirements of Compare ) which returns true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function object must not modify the objects passed to it. 
Type requirements  
BidirIt must meet the requirements of ValueSwappable and BidirectionalIterator .
 
The type of dereferenced BidirIt must meet the requirements of MoveAssignable and MoveConstructible .

[edit] Return value
(none)
[edit] Complexity
Exactly N1 comparisons if enough additional memory is available, otherwise N·log(N) where N = std::distance(first, last).
[edit] 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,
 if
policy
is std::parallel_vector_execution_policy, std::terminate is called  if
policy
is std::sequential_execution_policy or std::parallel_execution_policy, the algorithm exits with an std::exception_list containing all uncaught exceptions. If there was only one uncaught exception, the algorithm may rethrow it without wrapping in std::exception_list. It is unspecified how much work the algorithm will perform before returning after the first exception was encountered.  if
policy
is some other type, the behavior is implementationdefined
 if
 If the algorithm fails to allocate memory (either for itself or to construct an std::exception_list when handling a user exception), std::bad_alloc is thrown.
[edit] Notes
This function attempts to allocate a temporary buffer, typically by calling std::get_temporary_buffer. If the allocation fails, the less efficient algorithm is chosen.
[edit] Example
The following code is an implementation of merge sort.
#include <vector> #include <iostream> #include <algorithm> template<class Iter> void merge_sort(Iter first, Iter last) { if (last  first > 1) { Iter middle = first + (last  first) / 2; merge_sort(first, middle); merge_sort(middle, last); std::inplace_merge(first, middle, last); } } int main() { std::vector<int> v{8, 2, 2, 0, 11, 11, 1, 7, 3}; merge_sort(v.begin(), v.end()); for(auto n : v) { std::cout << n << ' '; } std::cout << '\n'; }
Output:
2 0 1 2 3 7 8 11 11
[edit] See also
merges two sorted ranges (function template)  
sorts a range into ascending order (function template)  
sorts a range of elements while preserving order between equal elements (function template)  
(parallelism TS) 
parallelized version of std::inplace_merge (function template) 