C++ set get_allocator()

C++ set get_allocator() function is used to return the copy of allocator object which helps to construct the set container.

Syntax

           allocator_type get_allocator() const; 		//until C++ 11
allocator_type get_allocator() const noexcept; 	//since C++ 11

Parameter

None

Return value

Returns an allocator associated with set container.

Complexity

Constant.

Iterator validity

No changes.

Data Races

The container is accessed.

Concurrently accessing the elements of set is safe.

Exception Safety

This function never throws exceptions.

Example 1

Let's see the simple example:

#include <iostream>
#include <set>

using namespace std;

int main(void) {
   set<double> m;   
   double *p;

   p = m.get_allocator().allocate(3);

   //size of double is 8
   cout << "Allocated size = " <<  sizeof(*p) * 4 << endl;

   return 0;
}

Output:

Allocated size = 32

Example 2

Let's see a simple example:

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  set<int> myset;
  int * p;
  unsigned int i;

  // allocate an array of 5 elements using myset's allocator:
  p=myset.get_allocator().allocate(5);

  // assign some values to array
  for (i=0; i<5; i++) p[i]=(i+1)*10;

  cout << "The allocated array contains:";
  for (i=0; i<5; i++) cout << ' ' << p[i];
  cout << '\n';

  myset.get_allocator().deallocate(p,5);

  return 0;
}

Output:

The allocated array contains: 10 20 30 40 50

Example 3

Let's see a simple example to check whether the allocators are interchangeable or not:

#include <set>  
#include <iostream>  
  
int main( )  
{  
   using namespace std;  
   set <int>::allocator_type s1_Alloc;  
   set <int>::allocator_type s2_Alloc;  
   set <double>::allocator_type s3_Alloc;  
   set <int>::allocator_type s4_Alloc;  
  
   // The following lines declare objects  
   // that use the default allocator.  
   set <int> s1;  
   set <int, allocator<int> > s2;  
   set <double, allocator<double> > s3;  
  
   s1_Alloc = s1.get_allocator( );  
   s2_Alloc = s2.get_allocator( );  
   s3_Alloc = s3.get_allocator( );  
  
   cout << "The number of integers that can be allocated"  
        << endl << "before free memory is exhausted: "  
        << s2.max_size( ) << "." << endl;  
  
   cout << "\nThe number of doubles that can be allocated"  
        << endl << "before free memory is exhausted: "  
        << s3.max_size( ) <<  "." << endl;  
  
   // The following line creates a set s4  
   // with the allocator of multiset s1.  
   set <int> s4( less<int>( ), s1_Alloc );  
  
   s4_Alloc = s4.get_allocator( );  
  
   // Two allocators are interchangeable if  
   // storage allocated from each can be  
   // deallocated by the other  
   if( s1_Alloc == s4_Alloc )  
   {  
      cout << "\nThe allocators are interchangeable."  
           << endl;  
   }  
   else  
   {  
      cout << "\nThe allocators are not interchangeable."  
           << endl;  
   }
   
   return 0;
}

Output:

The number of integers that can be allocated
before free memory is exhausted: 461168601842738790.

The number of doubles that can be allocated
before free memory is exhausted: 461168601842738790.

The allocators are interchangeable.

Example 4

Let's see a simple example:

#include <iostream>
 #include <set>

using namespace std;

int  main () 
{ 
  set < int >  c ; 
  int *  p ;

  p  =  c . get_allocator () . allocate ( 2 );

  p [ 0 ]  =  42 ; 
  p [ 1 ]  =  43 ;

  cout  <<  p [ 0 ]  <<  ", "  <<  p [ 1 ]  <<  endl ;

  c . get_allocator () . deallocate ( p ,  2 ); 
}

Output: