From cppreference.com
template<class...Args>iteratoremplace(const_iteratorpos,Args&&...args);(since C++11)Inserts a new element into the container directly before pos.
The element is constructed through
std::allocator_traits::construct
, which typically uses placement new to construct the element in-place at a location provided by the container. However, if the required location has been occupied by an existing element, the inserted element is constructed at another location at first, and then move assigned into the required location.
The arguments args... are forwarded to the constructor as std::forward<Args>(args).... args... may directly or indirectly refer to a value in the container.
All iterators (including the
iterator) are invalidated. References are invalidated too, unless pos==
or pos==
, in which case they are not invalidated.
Parameters
pos - iterator before which the new element will be constructed args - arguments to forward to the constructor of the element Type requirements -T must meet the requirements of
,
and
. Return value
Iterator pointing to the emplaced element.
Complexity
Linear in the lesser of the distances between pos and either of the ends of the container.
Exceptions
If an exception is thrown other than by the copy constructor, move constructor, assignment operator, or move assignment operator of the T, or if an exception is thrown while emplace is used to insert a single element at the either end, there are no effects (strong exception guarantee).
Otherwise, the effects are unspecified.
Example
Run this code
#include<iostream>#include<string>#include<deque>structA{std::strings;A(std::stringstr):s(std::move(str)){std::cout<<" constructed\n";}A(constA&o):s(o.s){std::cout<<" copy constructed\n";}A(A&&o):s(std::move(o.s)){std::cout<<" move constructed\n";}A&operator=(constA&other){s=other.s;std::cout<<" copy assigned\n";return*this;}A&operator=(A&&other){s=std::move(other.s);std::cout<<" move assigned\n";return*this;}};intmain(){std::deque<A>container;std::cout<<"construct 2 times A:\n";Atwo{"two"};Athree{"three"};std::cout<<"emplace:\n";container.emplace(container.end(),"one");std::cout<<"emplace with A&:\n";container.emplace(container.end(),two);std::cout<<"emplace with A&&:\n";container.emplace(container.end(),std::move(three));std::cout<<"content:\n";for(constauto&obj:container)std::cout<<' '<<obj.s;std::cout<<'\n';}Output:
construct 2 times A: constructed constructed emplace: constructed emplace with A&: copy constructed emplace with A&&: move constructed content: one two three Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++11 it was unclear whether the arguments can refer to the container made clear See also