std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::operator=
unordered_map& operator=
(
const unordered_map& other )
;
|
(1) | (since C++11) |
(2) | ||
unordered_map& operator=
( unordered_map&& other )
;
|
(since C++11) (until C++17) |
|
unordered_map& operator=
( unordered_map&& other )
noexcept
(
/* see below */
)
;
|
(since C++17) | |
unordered_map& operator=
(
std::initializer_list
<value_type> ilist )
;
|
(3) | (since C++11) |
Replaces the contents of the container.
Parameters
other | - | another container to use as data source |
ilist | - | initializer list to use as data source |
Return value
*this
Complexity
Exceptions
1-3) May throw implementation-defined exceptions.
|
(until C++17) |
1,3) May throw implementation-defined exceptions.
2)
noexcept specification:
noexcept
(
std::allocator_traits
<Allocator>
::
is_always_equal
::
value
&&
std::is_nothrow_move_assignable
<Hash>
::
value
|
(since C++17) |
Notes
After container move assignment (overload (2)), unless element-wise move assignment is forced by incompatible allocators, references, pointers, and iterators (other than the end iterator) to other
remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321
Example
The following code uses operator= to assign one std::unordered_map
#include <initializer_list> #include <iostream> #include <iterator> #include <unordered_map> #include <utility> void print(auto const comment, auto const& container) { auto size = std::size(container); std::cout << comment << "{ "; for (auto const& [key, value] : container) std::cout << '{' << key << ',' << value << (--size ? "}, " : "} "); std::cout << "}\n"; } int main() { std::unordered_map<int, int> x{{1,1}, {2,2}, {3,3}}, y, z; const auto w = {std::pair<const int, int>{4,4}, {5,5}, {6,6}, {7,7}}; std::cout << "Initially:\n"; print("x = ", x); print("y = ", y); print("z = ", z); std::cout << "Copy assignment copies data from x to y:\n"; y = x; print("x = ", x); print("y = ", y); std::cout << "Move assignment moves data from x to z, modifying both x and z:\n"; z = std::move(x); print("x = ", x); print("z = ", z); std::cout << "Assignment of initializer_list w to z:\n"; z = w; print("w = ", w); print("z = ", z); }
Possible output:
Initially: x = { {3,3}, {2,2}, {1,1} } y = { } z = { } Copy assignment copies data from x to y: x = { {3,3}, {2,2}, {1,1} } y = { {3,3}, {2,2}, {1,1} } Move assignment moves data from x to z, modifying both x and z: x = { } z = { {3,3}, {2,2}, {1,1} } Assignment of initializer_list w to z: w = { {4,4}, {5,5}, {6,6}, {7,7} } z = { {7,7}, {6,6}, {5,5}, {4,4} }
See also
constructs the unordered_map (public member function) |