• InputIterator1's value type is convertible to StrictWeakOrdering's argument type.
• InputIterator1's value type is convertible to a type in OutputIterator's set of value types.
Preconditions For the first version:
• [first1, last1) is a valid range.
• [first1, last1) is in ascending order. That is, for every pair of iterators i and j in [first1, last1) such that i precedes j, *j < *i is false.
• [first2, last2) is a valid range.
• [first2, last2) is in ascending order. That is, for every pair of iterators i and j in [first2, last2) such that i precedes j, *j < *i is false.
• The ranges [first1, last1) and [result, result + (last1 – first1) + (last2 – first2)) do not overlap.
• The ranges [first2, last2) and [result, result + (last1 – first1) + (last2 – first2)) do not overlap.
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last1 – first1) + (last2 – first2)) is a valid range.
For the second version:
• [first1, last1) is a valid range.
• [first1, last1) is in ascending order. That is, for every pair of iterators i and j in [first1, last1) such that i precedes j, comp(*j, *i) is false.
• [first2, last2) is a valid range.
• [first2, last2) is in ascending order. That is, for every pair of iterators i and j in [first2, last2) such that i precedes j, comp(*j, *i) is false.
• The ranges [first1, last1) and [result, result + (last1 – first1) + (last2 – first2)) do not overlap.
• The ranges [first2, last2) and [result, result + (last1 – first1) + (last2 – first2)) do not overlap.
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last1 – first1) + (last2 – first2)) is a valid range.
Complexity Linear. No comparisons if both [first1, last1) and [first2, last2) are empty ranges, otherwise at most (last1 – first1) + (last2 – first2) – 1 comparisons.
Example int main() {
int A1[] = { 1, 3, 5, 7 };
int A2[] = { 2, 4, 6, 8 };
const int N1 = sizeof(A1) / sizeof(int);
const int N2 = sizeof(A2) / sizeof(int);
merge(A1, A1 + N1, A2, A2 + N2, ostream_iterator<int>(cout, ' '));
// The output is '1 2 3 4 5 6 7 8'
}
Notes [1] Note that you may use an ordering that is a strict weak ordering but not a total ordering; that is, there might be values x and y such that x < y, x > y, and x == y are all false. (See the LessThan Comparable requirements for a more complete discussion.) Two elements x and y are equivalent if neither x < y nor y < x. If you're using a total ordering, however (if you're using strcmp, for example, or if you're using ordinary arithmetic comparison on integers), then you can ignore this technical distinction: for a total ordering, equality and equivalence are the same.
See also inplace_merge, set_union, sort
Category: algorithms
Component type: function
Prototype Inplace_merge is an overloaded name: there are actually two inplace_merge functions.
template <class BidirectionalIterator>
inline void inplace_merge(BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last);
template <class BidirectionalIterator, class StrictWeakOrdering>
inline void inplace_merge(BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last, StrictWeakOrdering comp);
Description Inplace_merge combines two consecutive sorted ranges [first, middle) and [middle, last) into a single sorted range [first, last). That is, it starts with a range [first, last) that consists of two pieces each of which is in ascending order, and rearranges it so that the entire range is in ascending order. Inplace_merge is stable, meaning both that the relative order of elements within each input range is preserved, and that for equivalent [1] elements in both input ranges the element from the first range precedes the element from the second.
The two versions of inplace_merge differ in how elements are compared. The first version uses operator<. That is, the input ranges and the output range satisfy the condition that for every pair of iterators i and j such that i precedes j, *j < *i is false. The second version uses the function object comp. That is, the input ranges and the output range satisfy the condition that for every pair of iterators i and j such that i precedes j, comp(*j, *i) is false.
Definition Defined in algo.h.
Requirements on types 
