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std::vector::emplace_back

提供: cppreference.com
< cpp‎ | container‎ | vector

 
 
 
std::vector
メンバ関数
Original:
Member functions
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vector::vector
vector::~vector
vector::operator=
vector::assign
vector::get_allocator
要素アクセスの循環参照を解除するために使用されている
Original:
Element access
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vector::at
vector::operator[]
vector::front
vector::back
vector::data(C++11)
イテレータ
Original:
Iterators
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vector::begin
vector::cbegin

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

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

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

(C++11)
容量
Original:
Capacity
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vector::empty
vector::size
vector::max_size
vector::reserve
vector::capacity
vector::shrink_to_fit(C++11)
修飾子
Original:
Modifiers
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vector::clear
vector::insert
vector::emplace(C++11)
vector::erase
vector::push_back
vector::emplace_back(C++11)
vector::pop_back
vector::resize
vector::swap
 
template< class... Args >
void emplace_back( Args&&... args );
(C++11およびそれ以降)
コンテナの最後に追加し、新しい要素。要素はその場で構成され、操作が実行されないコピーや移動、すなわちません。要素のコンストラクタは、関数に供給され、全く同じ引数で呼び出されます.
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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If the new size() is greater than capacity(), all iterators and references are invalidated. Otherwise no iterators and references are invalidated.

目次

[編集] パラメータ

args -
要素のコンストラクタに転送するための引数
Original:
arguments to forward to the constructor of the element
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[編集] 値を返します

(なし)
Original:
(none)
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[編集] 複雑

定数.
Original:
Constant.
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[編集]

次のコードは、emplace_backにタイプPresidentのオブジェクトを追加するstd::vectorを使用しています。それはどのようにemplace_back転送パラメータPresidentコンストラクタに示し、emplace_backを使用してpush_backを使用するときに必要とされる余分のコピーや移動操作を回避する方法を示し.
Original:
The following code uses emplace_back to append an object of type President to a std::vector. 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 <vector>
#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::vector<President> elections;
    std::cout << "emplace_back:\n";
    elections.emplace_back("Nelson Mandela", "South Africa", 1994);
 
    std::vector<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.

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