std::list::emplace_back

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

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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

 

template< class... Args > void emplace_back( Args&&... args );		(since C++11)

Appends a new element to the end of the container. The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element is called with exactly the same arguments that are supplied to the function.

No iterators or references are invalidated.

Parameters

args

-

arguments to forward to the constructor of the element

Return value

(none)

Complexity

Constant.

Exceptions

If an exception is thrown, this function has no effect (strong exception guarantee).

Example

The following code uses emplace_back to append an object of type President to a std::list. It demonstrates how emplace_back forwards parameters to the President constructor and shows how using emplace_back avoids the extra copy or move operation required when using push_back.

Run this code

#include <list>
#include <string>
#include <iostream>
 
struct President
{
    std::string name;
    std::string country;
    int year;
 
    President(std::string p_name, std::string p_country, int p_year)
        : name(std::move(p_name)), country(std::move(p_country)), year(p_year)
    {
        std::cout << "I am being constructed.\n";
    }
    President(President&& other)
        : name(std::move(other.name)), country(std::move(other.country)), year(other.year)
    {
        std::cout << "I am being moved.\n";
    }
    President& operator=(const President& other) = default;
};
 
int main()
{
    std::list<President> elections;
    std::cout << "emplace_back:\n";
    elections.emplace_back("Nelson Mandela", "South Africa", 1994);
 
    std::list<President> reElections;
    std::cout << "\npush_back:\n";
    reElections.push_back(President("Franklin Delano Roosevelt", "the USA", 1936));
 
    std::cout << "\nContents:\n";
    for (President const& president: elections) {
        std::cout << president.name << " was elected president of "
                  << president.country << " in " << president.year << ".\n";
    }
    for (President const& president: reElections) {
        std::cout << president.name << " was re-elected president of "
                  << president.country << " in " << president.year << ".\n";
    }
}

Output:

emplace_back:
I am being constructed.
 
push_back:
I am being constructed.
I am being moved.
 
Contents:
Nelson Mandela was elected president of South Africa in 1994.
Franklin Delano Roosevelt was re-elected president of the USA in 1936.

See also

push_back

adds elements to the end (public member function)