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std::deque::emplace_back

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< cpp‎ | container‎ | deque

 
 
 
std :: deque
Les fonctions membres
Original:
Member functions
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deque::deque
deque::~deque
deque::operator=
deque::assign
deque::get_allocator
Elément d'accès
Original:
Element access
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deque::front
deque::back
Les itérateurs
Original:
Iterators
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deque::begin
deque::cbegin

(C++11)
deque::end
deque::cend

(C++11)
deque::rbegin
deque::crbegin

(C++11)
deque::rend
deque::crend

(C++11)
Capacité
Original:
Capacity
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deque::empty
deque::size
deque::max_size
deque::shrink_to_fit
Modificateurs
Original:
Modifiers
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deque::clear
deque::insert
deque::emplace
deque::erase
deque::push_front
deque::emplace_front
deque::pop_front
deque::push_back
deque::emplace_back
deque::pop_back
deque::resize
deque::swap
 
template< class... Args >
void emplace_back( Args&&... args );
(depuis C++11)
Ajoute un nouvel élément à la fin du récipient. L'élément est réalisé in-situ, c'est à dire pas de copie ou les opérations de déplacement sont effectuées. Le constructeur de l'élément est appelée avec exactement les mêmes arguments qui sont fournis à la fonction .
Original:
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.
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All iterators are invalidated. No references are invalidated.

Sommaire

[modifier] Paramètres

args -
arguments à transmettre au constructeur de l'élément
Original:
arguments to forward to the constructor of the element
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[modifier] Retourne la valeur

(Aucun)
Original:
(none)
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[modifier] Complexité

Constant .
Original:
Constant.
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[modifier] Exemple

Le code suivant utilise emplace_back d'ajouter un objet de President type à un std::deque. Il démontre comment emplace_back transmet les paramètres au constructeur President et montre comment l'utilisation emplace_back évite la copie supplémentaire ou un déplacement nécessaire lorsque vous utilisez push_back .
Original:
The following code uses emplace_back to append an object of type President to a std::deque. 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.
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#include <deque>
#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::deque<President> elections;
    std::cout << "emplace_back:\n";
    elections.emplace_back("Nelson Mandela", "South Africa", 1994);
 
    std::deque<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";
    }
}

Résultat :

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.

[modifier] Voir aussi

ajoute des éléments à la fin
Original:
adds elements to the end
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(fonction membre publique) [edit]