您好,登錄后才能下訂單哦!
C++ 中"emplace_back" 與 "push_back" 的區別
emplace_back和push_back都是向容器內添加數據.
對于在容器中添加類的對象時, 相比于push_back,emplace_back可以避免額外類的復制和移動操作.
"emplace_back avoids the extra copy or move operation required when using push_back."
參見: http://en.cppreference.com/w/cpp/container/vector/emplace_back
注意下面代碼中的emplace_back和push_back的添加方式(VS2012下編譯通過):
#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); }; int main() { std::vector<President> elections; std::cout << "emplace_back:\n"; elections.emplace_back("Nelson Mandela", "South Africa", 1994); //沒有類的創建 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"; } }
感謝閱讀,希望能幫助到大家,謝謝大家對本站的支持!
免責聲明:本站發布的內容(圖片、視頻和文字)以原創、轉載和分享為主,文章觀點不代表本網站立場,如果涉及侵權請聯系站長郵箱:is@yisu.com進行舉報,并提供相關證據,一經查實,將立刻刪除涉嫌侵權內容。