C++ std::list::get_allocator

The std::list::get_allocator function returns a copy of the allocator used by the std::list. An allocator is responsible for managing the memory used by the list. This function is particularly useful when you need to create other containers with the same allocator as the current list.

Syntax of std::list::get_allocator

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allocator_type get_allocator() const;

Parameters

This function does not accept any parameters.

Return Value

The function returns a copy of the allocator object used by the list. The allocator object can then be used to allocate memory for other containers or custom memory management tasks.

Exceptions

The std::list::get_allocator function does not throw exceptions. It provides a no-throw guarantee.

Examples for std::list::get_allocator

Example 1: Using get_allocator to Allocate Memory

This example demonstrates how to use get_allocator to allocate memory for an array of integers:

Program

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#include <iostream>
#include <list>

int main() {
    std::list<int> myList;

    // Get the allocator for the list
    std::list<int>::allocator_type allocator = myList.get_allocator();

    // Allocate memory for 5 integers
    int* array = allocator.allocate(5);

    // Construct elements in the allocated memory
    for (int i = 0; i < 5; ++i) {
        allocator.construct(&array[i], i + 1); // Construct elements with values 1, 2, 3, 4, 5
    }

    // Print the constructed array
    std::cout << "Allocated and constructed array: ";
    for (int i = 0; i < 5; ++i) {
        std::cout << array[i] << " ";
    }
    std::cout << std::endl;

    // Destroy and deallocate the memory
    for (int i = 0; i < 5; ++i) {
        allocator.destroy(&array[i]); // Destroy each element
    }
    allocator.deallocate(array, 5); // Deallocate the memory

    return 0;
}

Explanation:

  1. A std::list named myList is created.
  2. The get_allocator function is called to retrieve the allocator used by the list.
  3. The allocator is used to allocate memory for an array of 5 integers.
  4. The construct method of the allocator is used to initialize the allocated memory with values 1, 2, 3, 4, 5.
  5. The constructed array is printed to the console.
  6. The destroy method is called to destruct the constructed elements, and the deallocate method frees the allocated memory.

Output:

Allocated and constructed array: 1 2 3 4 5

Example 2: Sharing an Allocator with Another Container

This example demonstrates how to use get_allocator to share the same allocator with another std::list:

Program

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#include <iostream>
#include <list>

int main() {
    std::list<int> list1 = {1, 2, 3};

    // Get the allocator from list1
    std::list<int>::allocator_type allocator = list1.get_allocator();

    // Use the allocator to create a new list with the same allocator
    std::list<int> list2(allocator);

    // Populate the second list
    list2.push_back(4);
    list2.push_back(5);
    list2.push_back(6);

    std::cout << "Contents of list1: ";
    for (const auto& elem : list1) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    std::cout << "Contents of list2: ";
    for (const auto& elem : list2) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. A std::list named list1 is initialized with elements {1, 2, 3}.
  2. The get_allocator function is used to retrieve the allocator of list1.
  3. A new std::list named list2 is created using the same allocator.
  4. Elements 4, 5, 6 are added to list2, and the contents of both lists are printed.

Output:

Contents of list1: 1 2 3
Contents of list2: 4 5 6