C++ STL unordered_set get_allocator() with Examples

The get_allocator() method of unordered_set is the part of Standard Template Library(STL) of C++. This method gets the stored allocator object and returns it.

Syntax:

allocator_type get_allocator() const;

where Allocator_type is the type of allocator used by the container.

Return Value: It returns the allocator object used to construct the container.

Exceptions: In this method, an Exception is thrown if any element comparison object throws an exception.

The below program illustrates the unordered_set::get_allocator() function

Program 1:

C++

// C++ program to demonstrate
// unordered_set get_allocator()

#include <iostream>
#include <unordered_set> // Their Library

using namespace std;
int main()
{

    //'c' is object of 'unordered_set'
    unordered_set<int> c;

    //'allocator_type' is inherit in 'unordered_set'
    //'a' is object of 'allocator_type'
    //'get_allocator()' is member of 'unordered_set'
    unordered_set<int>::allocator_type a
        = c.get_allocator();

    // Comparing the Allocator with Pair<int, int>
    cout << "Is allocator Pair<int, int> : " << boolalpha
         << (a == allocator<pair<int, int> >());

    return 0;
}

Output

Is allocator Pair<int, int> : true

Complexity: It takes constant(O(1)) time of complexity to perform an operation.

Program 2 : 

C++

// C++ program to demonstrate
// unordered_set get_allocator()

#include <iostream>
#include <unordered_map> // Their Library

using namespace std;

int main(void)
{
    unordered_map<char, int> um;
    pair<const char, int>* a;

    a = um.get_allocator().allocate(8);

    cout << "Allocated size = " << sizeof(*a) * 8 << endl;

    return 0;
}

Output

Allocated size = 64