std::multimap operator=
- since C++17
- since C++11
- since C++98
// (1) Non const version only
multimap& operator=( const multimap& other );
// (2) Non const version only
multimap& operator=( multimap&& other ) noexcept(/* see below */);
// (3) Non const version only
multimap& operator=( std::initializer_list<value_type> ilist );
// (1) Non const version only
multimap& operator=( const multimap& other );
// (2) Non const version only
multimap& operator=( multimap&& other );
// (3) Non const version only
multimap& operator=( std::initializer_list<value_type> ilist );
// (1) Non const version only
multimap& operator=( const multimap& other );
Replaces the contents of the containter.
Parameters
other
- another container to use as data sourceilist
- initializer list to use as data source
Return value
A reference to the container, *this
.
Exceptions
- since C++17
- 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<Compare>::value)
Complexity
- (1) Linear in the size of
*this
andother
- O(size() + other.size()). - (2)
Linear in the size of*this
- O(size()). If the allocators do not compare equal and do not propagate - linear in the size of*this
andother
- O(size() + other. - (3)
O(N log N) in general, where N issize() + ilist.size()
. Linear ifilist
is sorted with respect tovalue_comp()
- O(size()).
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.requirements.general]/12
, and a more direct guarantee is under consideration via LWG 2321.
Example
#include <map>
#include <iterator>
#include <iostream>
#include <utility>
#include <initializer_list>
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::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);
}
Initially:
x = { {1,1}, {2,2}, {3,3} }
y = { }
z = { }
Copy assignment copies data from x to y:
x = { {1,1}, {2,2}, {3,3} }
y = { {1,1}, {2,2}, {3,3} }
Move assignment moves data from x to z, modifying both x and z:
x = { }
z = { {1,1}, {2,2}, {3,3} }
Assignment of initializer_list w to z:
w = { {4,4}, {5,5}, {6,6}, {7,7} }
z = { {4,4}, {5,5}, {6,6}, {7,7} }
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