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std::list::emplace_back

Da cppreference.com.
< cpp‎ | container‎ | list

 
 
 
std::list
Membri funzioni
Original:
Member functions
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list::list
list::~list
list::operator=
list::assign
list::get_allocator
Elemento accesso
Original:
Element access
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list::front
list::back
Iteratori
Original:
Iterators
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list::begin
list::cbegin

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

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

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

(C++11)
Capacità
Original:
Capacity
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list::empty
list::size
list::max_size
Modificatori
Original:
Modifiers
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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
Operazioni
Original:
Operations
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list::merge
list::splice
list::remove
list::remove_if
list::reverse
list::unique
list::sort
 
template< class... Args >
void emplace_back( Args&&... args );
(dal C++11)
Aggiunge un nuovo elemento alla fine del contenitore. L'elemento è costruito sul posto, cioè non copia o operazioni di spostamento vengono eseguite. Il costruttore dell'elemento viene chiamato con esattamente gli stessi argomenti che vengono forniti alla funzione.
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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No iterators or references are invalidated.

Indice

[modifica] Parametri

args -
argomenti da inoltrare al costruttore dell'elemento
Original:
arguments to forward to the constructor of the element
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[modifica] Valore di ritorno

(Nessuno)
Original:
(none)
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[modifica] Complessità

Costante.
Original:
Constant.
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[modifica] Esempio

Il codice seguente utilizza emplace_back per aggiungere un oggetto di tipo a una President std::list. Dimostra come emplace_back inoltra parametri al costruttore President e mostra come utilizzare emplace_back evita la copia in più o operazione di spostamento necessaria quando si utilizza push_back .
Original:
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.
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#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.

[modifica] Vedi anche

aggiunge elementi alla fine
Original:
adds elements to the end
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(membro pubblico funzione) [edit]