public member function
<list>

std::list::operator=

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

Copies all the elements from x into the container.

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 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.

Any elements held in the container before the call are either assigned to or destroyed.

Parameters

x
A list object of the same type (i.e., with the same template parameters, T 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 list as an alias of its first template parameter (T).

Return value

*this

Example

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// assignment operator with lists
#include <iostream>
#include <list>

int main ()
{
  std::list<int> first (3);      // list of 3 zero-initialized ints
  std::list<int> second (5);     // list of 5 zero-initialized ints

  second = first;
  first = std::list<int>();

  std::cout << "Size of first: " << int (first.size()) << '\n';
  std::cout << "Size of second: " << int (second.size()) << '\n';
  return 0;
}

Both list containers of int elements are initialized to sequences with different sizes. Then, second is assigned to first, so both are now equal and with a size of 3. And then, first is assigned to a newly constructed empty container object, so its size is finally 0. Output:
Size of first: 0
Size of second: 3

Complexity

Linear in size.

Iterator validity

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

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

list::list
Construct list (public member function )
list::assign
Assign new content to container (public member function )

C++