std::map::operator=

 

C++

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std::map

Member functions

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map::operator=

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Element access

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map::key_comp

map::value_comp

 

map& operator=( const map& other );	(1)
map& operator=( map&& other );	(2)	(since C++11)
map& operator=( std::initializer_list<value_type> ilist );	(3)	(since C++11)

Replaces the contents of the container.

1) Copy assignment operator. Replaces the contents with a copy of the contents of other.

2) Move assignment operator. Replaces the contents with those of other using move semantics (i.e. the data in other is moved from other into this container). other is in a valid but unspecified state afterwards.

3) Replaces the contents with those identified by initializer list ilist.

Parameters

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

Return value

*this

Complexity

1) Linear in the size of the other.

2) Constant.

3) Linear in the size of ilist.

Example

The following code uses to assign one std::map to another:

run this code

#include <map>
#include <iostream>
 
void display_sizes(const std::map<int, int> &nums1,
                   const std::map<int, int> &nums2,
                   const std::map<int, int> &nums3)
{
    std::cout << "nums1: " << nums1.size() 
              << " nums2: " << nums2.size()
              << " nums3: " << nums3.size() << '\n';
}
 
int main()
{
    std::map<int, int> nums1 {{3, 1}, {4, 1}, {5, 9}, 
                              {6, 1}, {7, 1}, {8, 9}};
    std::map<int, int> nums2; 
    std::map<int, int> nums3;
 
    std::cout << "Initially:\n";
    display_sizes(nums1, nums2, nums3);
 
    // copy assignment copies data from nums1 to nums2
    nums2 = nums1;
 
    std::cout << "After assigment:\n"; 
    display_sizes(nums1, nums2, nums3);
 
    // move assignment moves data from nums1 to nums3,
    // modifying both nums1 and nums3
    nums3 = std::move(nums1);
 
    std::cout << "After move assigment:\n"; 
    display_sizes(nums1, nums2, nums3);
}

Output:

Initially:
nums1: 6 nums2: 0 nums3: 0
After assigment:
nums1: 6 nums2: 6 nums3: 0
After move assigment:
nums1: 0 nums2: 6 nums3: 6

See also

(constructor)	constructs the map (public member function)