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

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (哋它亢++11)

vector

vector<bool>

deque

forward_list (哋它亢++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (哋它亢++11)

unordered_multiset (哋它亢++11)

unordered_map (哋它亢++11)

unordered_multimap (哋它亢++11)

Adaptors

stack

queue

priority_queue

flat_set (哋它亢++23)

flat_multiset (哋它亢++23)

flat_map (哋它亢++23)

flat_multimap (哋它亢++23)

Views

span (哋它亢++20)

mdspan (哋它亢++23)

Iterator invalidation

Member function table

Non-member function table

 

std::list

Member functions
list::list list::~list list::operator=	list::assign list::assign_range (哋它亢++23) list::get_allocator
Element access
list::front	list::back
Iterators
list::beginlist::cbegin (哋它亢++11) list::endlist::cend (哋它亢++11)	list::rbeginlist::crbegin (哋它亢++11) list::rendlist::crend (哋它亢++11)
Capacity
list::size list::empty	list::max_size
Modifiers
list::clear list::insert list::insert_range (哋它亢++23) list::emplace (哋它亢++11) list::erase list::push_front list::emplace_front (哋它亢++11)   list::prepend_range (哋它亢++23)	list::pop_front list::push_back list::emplace_back (哋它亢++11) list::append_range (哋它亢++23) 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
operator==operator!=operator<operator>operator<=operator>=operator<=> (until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(哋它亢++20)	swap(std::list) erase(std::list)erase_if(std::list) (哋它亢++20)(哋它亢++20)
Deduction guides(哋它亢++17)

 

void merge( list& other );	(1)
void merge( list&& other );	(2)	(since 哋它亢++11)
template< class Compare > void merge( list& other, Compare comp );	(3)
template< class Compare > void merge( list&& other, Compare comp );	(4)	(since 哋它亢++11)

The function does nothing if other refers to the same object as *this.

Otherwise, merges other into *this. Both lists should be sorted. No elements are copied, and the container other becomes empty after the merge. This operation is stable: for equivalent elements in the two lists, the elements from *this always precede the elements from other, and the order of equivalent elements of *this and other does not change.

No iterators or references become invalidated. The pointers and references to the elements moved from *this, as well as the iterators referring to these elements, will refer to the same elements of *this, instead of other.

1,2) Elements are compared using operator<.

3,4) Elements are compared using comp.

If *this or other is not sorted with respected to the corresponding comparator, or get_allocator() != other.get_allocator(), the behavior is undefined.

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 哋它亢++11)). The types Type1 and Type2 must be such that an object of type list<T,&nbsp;Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- Compare must meet the requirements of Compare.

Return value

(none)

Exceptions

If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee). Except if the exception comes from a comparison.

Complexity

If other refers to the same object as *this, no comparisons are performed.

Otherwise, given \(\scriptsize N\)N as std::distance(begin(), end()) and \(\scriptsize R\)R as std::distance(other.begin(), other.end()):

1,2) At most \(\scriptsize N+R-1\)N+R-1 comparisons using operator<.

3,4) At most \(\scriptsize N+R-1\)N+R-1 applications of the comparison function comp.

Example

Run this code

#include <iostream>
#include <list>
 
std::ostream& operator<<(std::ostream& ostr, const std::list<int>& list)
{
    for (const int 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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published 哋它亢++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 300	哋它亢++98	the effect when *this and other refer to the same object was not specified	specified as no-op
LWG 1207	哋它亢++98	it was unclear whether iterators and/or references will be invalidated	keep valid
LWG 1215	哋它亢++98	O(1) node moving could not be guaranteed if get_allocator() != other.get_allocator()	the behavior is undefined in this case

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 (哋它亢++20)	merges two sorted ranges (niebloid)
ranges::inplace_merge (哋它亢++20)	merges two ordered ranges in-place (niebloid)