< cpp‎ | algorithm
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Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
C library

Template:ddcl list begin <tr class="t-dsc-header">

Defined in header <algorithm>

<td></td> <td></td> </tr> <tr class="t-dcl ">

<td >
template< class BidirIt >
void inplace_merge( BidirIt first, BidirIt middle, BidirIt last );

<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">

<td >
template< class BidirIt, class Compare>
void inplace_merge( BidirIt first, BidirIt middle, BidirIt last, Compare comp );

<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end

Merges two consecutive sorted ranges [first, middle) and [middle, last) into one sorted range [first, last). The order of equal elements is guaranteed to be preserved. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.



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
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than 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.
The types Type1 and Type2 must be such that an object of type BidirIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
BidirIt must meet the requirements of ValueSwappable and BidirectionalIterator.
The type of dereferenced BidirIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value



Exactly N-1 comparisons if enough additional memory is available, otherwise N·log(N) where N = std::distance(first, last).


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.


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';


-2 0 1 2 3 7 8 11 11

See also

Template:cpp/algorithm/dcl list mergeTemplate:cpp/algorithm/dcl list sortTemplate:cpp/algorithm/dcl list stable sort