std::list<T,Allocator>::merge

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

span (C++20)

 

std::list

Member functions

list::list

list::~list

list::operator=

list::assign

list::get_allocator

Element access

list::front

list::back

Iterators

list::beginlist::cbegin (C++11)

list::endlist::cend (C++11)

list::rbeginlist::crbegin (C++11)

list::rendlist::crend (C++11)

Capacity

list::empty

list::size

list::max_size

Modifiers

list::clear

list::insert

list::emplace (C++11)

list::erase

list::push_front

list::emplace_front (C++11)

list::pop_front

list::push_back

list::emplace_back (C++11)

list::pop_back

list::resize

list::swap

Operations

list::merge

list::splice

list::removelist::remove_if

list::reverse

list::unique

list::sort

Non-member functions

std::swap

eraseerase_if (C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Deduction guides(C++17)

 

void merge( list& other );	(1)
void merge( list&& other );	(1)	(since C++11)
template <class Compare> void merge( list& other, Compare comp );	(2)
template <class Compare> void merge( list&& other, Compare comp );	(2)	(since C++11)

Merges two sorted lists into one. The lists should be sorted into ascending order.

No elements are copied. The container other becomes empty after the operation. The function does nothing if other refers to the same object as *this. If get_allocator() != other.get_allocator(), the behavior is undefined. No iterators or references become invalidated, except that the iterators of moved elements now refer into *this, not into other. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

This operation is stable: for equivalent elements in the two lists, the elements from *this shall always precede the elements from other, and the order of equivalent elements of *this and other does not change.

Parameters

other	-	another container to merge
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); While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy (since C++11)). The types Type1 and Type2 must be such that an object of type list<T,Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​

Return value

(none)

Exceptions

If an exception is thrown, this function has no effect (strong exception guarantee), except if the exception comes from the comparison function.

Complexity

At most std::distance(begin(), end()) + std::distance(other.begin(), other.end()) - 1 comparisons.

Example

Run this code

#include <iostream>
#include <list>
 
std::ostream& operator<<(std::ostream& ostr, const std::list<int>& list)
{
    for (const auto &i : list) {
        ostr << ' ' << i;
    }
    return ostr;
}
 
int main()
{
    std::list<int> list1 = { 5,9,1,3,3 };
    std::list<int> list2 = { 8,7,2,3,4,4 };
 
    list1.sort();
    list2.sort();
    std::cout << "list1:  " << list1 << '\n';
    std::cout << "list2:  " << list2 << '\n';
    list1.merge(list2);
    std::cout << "merged: " << list1 << '\n';
}

Output:

list1:   1 3 3 5 9
list2:   2 3 4 4 7 8
merged:  1 2 3 3 3 4 4 5 7 8 9

See also

splice	moves elements from another list (public member function)
merge	merges two sorted ranges (function template)
inplace_merge	merges two ordered ranges in-place (function template)
ranges::merge (C++20)	merges two sorted ranges (niebloid)
ranges::inplace_merge (C++20)	merges two ordered ranges in-place (niebloid)