C++ scoped_allocator::allocate() Function

The std::scoped_allocator::allocate() function in C++, allows for memory allocation within a scope, ensuring that the memory is properly managed and released. It is the part of the scoped_allocator_adaptor class, which adapts an allocator to manage memory across multiple levels of containers.

It provides a mechanism for allocating memory for a specified number of elements, using the allocated memory fro the provided allocator.

Syntax

Following is the syntax for std::scoped_allocator::allocate() function.

pointer allocate( size_type n );
or
pointer allocate( size_type n, const_void_pointer hint );

Parameters

• n − It indicates the number of objects to allocate storage for.
• hint − It indicates the pointer to a nearby memory location.

Return Value

This function returns the pointer to the allocated storage.

Example 1

Let's look at the following example, where we are going to allocate the memory for a single integer using the allocate().

#include <iostream>
#include <memory>
#include <scoped_allocator>
int main() {
   std::allocator < int > x;
   std::scoped_allocator_adaptor < std::allocator < int >> y(x);
   int * ptr = y.allocate(1);
   x.construct(ptr, 1121);
   std::cout << "Allocated value: " << * ptr << std::endl;
   x.destroy(ptr);
   y.deallocate(ptr, 1);
   return 0;
}

Output

Output of the above code is as follows −

Allocated value: 1121

Example 2

Consider the following example, where we are going to allocate memory for an array of 6 integers, Each element is initialized using the construct(), and the values are printed.

#include <iostream>
#include <memory>
#include <scoped_allocator>
int main() {
   std::allocator < int > a;
   std::scoped_allocator_adaptor < std::allocator < int >> b(a);
   int * array = b.allocate(5);
   for (int x = 0; x < 6; ++x) {
      a.construct( & array[x], x * 11);
   }
   for (int x = 0; x < 6; ++x) {
      std::cout << array[x] << " ";
   }
   std::cout << std::endl;
   for (int x = 0; x < 6; ++x) {
      a.destroy( & array[x]);
   }
   b.deallocate(array, 6);
   return 0;
}

Output

Output of the above code is as follows −

0 11 22 33 44 55