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public member function
<map>

std::multimap::operator=

copy (1)
 multimap& operator= (const multimap& x);
copy (1)
multimap& operator= (const multimap& x);
move (2)
multimap& operator= (multimap&& x);
initializer list (3)
multimap& operator= (initializer_list<value_type> il);
Copy container content
Assigns new contents to the container, replacing its current content.

Copies all the elements from x into the container, changing its size accordingly.

The container preserves its current allocator, which is used to allocate additional storage if needed.
The copy assignment (1) copies all the elements from x into the container (with x preserving its contents).

The move assignment (2) moves the elements of x into the container (x is left in an unspecified but valid state).

The initializer list assignment (3) copies the elements of il into the container.

The new container size is the same as the size of x (or il) before the call.

The container preserves its current allocator, except if the allocator traits indicate x's allocator should propagate. This allocator is used (through its traits) to allocate or deallocate if there are changes in storage requirements, and to construct or destroy elements, if needed.

The elements stored in the container before the call are either assigned to or destroyed.

Parameters

x
A multimap object of the same type (i.e., with the same template parameters, key, T, Compare and Alloc).
il
An initializer_list object. The compiler will automatically construct such objects from initializer list declarators.
Member type value_type is the type of the elements in the container, defined in multimap as an alias of pair<const key_type, mapped_type> (see multimap member types).

Return value

*this

Example

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// assignment operator with multimaps
#include <iostream>
#include <map>

int main ()
{
  std::multimap<char,int> foo,bar;

  foo.insert(std::make_pair('x',32));
  foo.insert(std::make_pair('y',64));
  foo.insert(std::make_pair('y',96));
  foo.insert(std::make_pair('z',128));

  bar = foo;                  // bar now contains 4 ints
  foo.clear();                // and first is now empty

  std::cout << "Size of foo: " << foo.size() << '\n';
  std::cout << "Size of bar: " << bar.size() << '\n';
  return 0;
}
Edit & Run

Output:
Size of foo: 0
Size of bar: 4

Complexity

For the copy assignment (1): Linear in sizes (destructions, copies).
For the move assignment (2): Linear in current container size (destructions).*
For the initializer list assignment (3): Up to logarithmic in sizes (destructions, move-assignments) -- linear if il is already sorted.
* Additional complexity for assignments if allocators do not propagate.

Iterator validity

All iterators, references and pointers related to this container are invalidated.

In the move assignment, iterators, pointers and references referring to elements in x are also invalidated.

Data races

All copied elements are accessed.
The move assignment (2) modifies x.
The container and all its elements are modified.

Exception safety

Basic guarantee: if an exception is thrown, the container is in a valid state.
If allocator_traits::construct is not supported with the appropriate arguments for the element constructions, or if value_type is not copy assignable (or move assignable for (2)), it causes undefined behavior.

See also

multimap::insert
Insert element (public member function )
multimap::find
Get iterator to element (public member function )
multimap::multimap
Construct multimap (public member function )

C++

Reference