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C++ 中"emplace_back" 与 "push_back" 的区别

2024-02-26 10:50:03 143

C++中"emplace_back"与"push_back"的区别

emplace_back和push_back都是向容器内添加数据.

对于在容器中添加类的对象时,相比于push_back,emplace_back可以避免额外类的复制和移动操作.

"emplace_backavoidstheextracopyormoveoperationrequiredwhenusingpush_back."

参见:http://en.cppreference.com/w/cpp/container/vector/emplace_back

注意下面代码中的emplace_back和push_back的添加方式(VS2012下编译通过):

#include
#include
#include

structPresident
{
std::stringname;
std::stringcountry;
intyear;

President(std::stringp_name,std::stringp_country,intp_year)
:name(std::move(p_name)),country(std::move(p_country)),year(p_year)
{
std::cout<<"Iambeingconstructed.\n";
}
President(President&&other)
:name(std::move(other.name)),country(std::move(other.country)),year(other.year)
{
std::cout<<"Iambeingmoved.\n";
}
President&operator=(constPresident&other);
};

intmain()
{
std::vectorelections;
std::cout<<"emplace_back:\n";
elections.emplace_back("NelsonMandela","SouthAfrica",1994);//没有类的创建

std::vectorreElections;
std::cout<<"\npush_back:\n";
reElections.push_back(President("FranklinDelanoRoosevelt","theUSA",1936));

std::cout<<"\nContents:\n";
for(Presidentconst&president:elections){
std::cout<
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C++ 中"emplace_back" 与 "push_back" 的区别

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