In STL, containers can change size dynamically. Allocator is an object that is responsible for dynamic memory allocation/deallocation. get_allocator() is used to allocate memory chunks of memory. It returns a copy of the allocator object associated with the container. It is defined in
vector,
map,
list,
set libraries.
Syntax:
allocator_type get_allocator() const;
Parameter Used:
This member function does not need any parameter to be passed.
Return Type:
It returns a copy of the allocator object associated with the vector.
Errors and Exceptions:
Never throws exceptions so we don't need any try-catch surrounding of it.
Time-Complexity:
Constant O(1).
Below programs illustrate the working of the function
1. std::vector::get_allocator() It returns a copy of the allocator object associated with the
vector.
CPP
// C++ program to show working
// of get_allocator function
#include <iostream>
#include <vector>
using namespace std;
// Function for allocating
char* Allocate(vector<char> arr, int size)
{
// allocate space for size(s) elements
return arr.get_allocator().allocate(size);
}
void Construct(vector<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
// construct values in-place on the array:
arr.get_allocator().construct(&point[iter],
iter + 97);
}
// Function for Deallocating
void deAllocate(vector<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
arr.get_allocator().destroy(&point[iter]);
// free allocated memory
arr.get_allocator().deallocate(point, size);
}
// Driver code
int main()
{
vector<char> array;
char* pointer;
int size = 8;
pointer = Allocate(array, size);
Construct(array, pointer, size);
cout << "Array elements: ";
for (int iter = 0; iter < size; ++iter)
cout << pointer[iter] << " ";
deAllocate(array, pointer, size);
return 0;
}
Output:
Array elements: a b c d e f g h
2. std::list::get_allocator() It returns a copy of the allocator object associated with the
list.
CPP
// C++ program to show working
// of get_allocator function
#include <iostream>
#include <list>
using namespace std;
// Function for allocating
char* Allocate(list<char> arr, int size)
{
// allocate space for size(s) elements
return arr.get_allocator().allocate(size);
}
void Construct(list<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
// construct values in-place on the array:
arr.get_allocator().construct(&point[iter],
iter + 97);
}
// Function for Deallocating
void deAllocate(list<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
arr.get_allocator().destroy(&point[iter]);
// free allocated memory
arr.get_allocator().deallocate(point, size);
}
// Driver code
int main()
{
list<char> array;
char* pointer;
int size = 8;
pointer = Allocate(array, size);
Construct(array, pointer, size);
cout << "Array elements: ";
for (int iter = 0; iter < size; ++iter)
cout << pointer[iter] << " ";
deAllocate(array, pointer, size);
return 0;
}
Output:
Array elements: a b c d e f g h
3. std::set::get_allocator() It returns a copy of the allocator object associated with the
set.
CPP
// C++ program to show working
// of get_allocator function
#include <iostream>
#include <set>
using namespace std;
// Function for allocating
char* Allocate(set<char> arr, int size)
{
// allocate space for size(s) elements
return arr.get_allocator().allocate(size);
}
void Construct(set<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
// construct values in-place on the array:
arr.get_allocator().construct(&point[iter],
iter + 97);
}
// Function for Deallocating
void deAllocate(set<char> arr,
char* point, int size)
{
for (int iter = 0; iter < size; ++iter)
arr.get_allocator().destroy(&point[iter]);
// free allocated memory
arr.get_allocator().deallocate(point, size);
}
// Driver code
int main()
{
set<char> array;
char* pointer;
int size = 8;
pointer = Allocate(array, size);
Construct(array, pointer, size);
cout << "Array elements: ";
for (int iter = 0; iter < size; ++iter)
cout << pointer[iter] << " ";
deAllocate(array, pointer, size);
return 0;
}
Output:
Array elements: a b c d e f g h
References:
http://www.cplusplus.com/reference/vector/vector/get_allocator/