std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::operator=

Since C++11

Replaces the contents of the container.

# Declarations

unordered_multimap& operator=( const unordered_multimap& other );

(since C++11)

unordered_multimap& operator=( unordered_multimap&& other );

(since C++11) (until C++17)

unordered_multimap& operator=( unordered_multimap&& other ) noexcept(/* see below */);

(since C++17)

unordered_multimap& operator=( std::initializer_list<value_type> ilist );

(since C++11)

# Parameters

other: another container to use as data source
ilist: initializer list to use as data source

# Return value

*this

# 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

#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_multimap<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);
}

# See also

(constructor)