[boost] New allocator that uses global memory

7 Jan 2020

      I propose a new allocator that uses global (i.e. static duration) memory.

Here is my current experimental code:

#include <cstddef>  /* size_t */
#include <new>  /* Only for bad_alloc */ 

static int this_translation_unit;  /* This serves the same purpose as 
__FILE__ */

template<typename T, std::size_t t_capacity, std::size_t t_counter, int 
*t_file = &this_translation_unit>
class StaticAllocator { 
protected: 

	static T buf[t_capacity];

public:

	typedef T value_type;

	template<typename U> 
	struct rebind { 
		typedef StaticAllocator<U, t_capacity, t_counter, t_file> 
other; 
	};

	T *allocate(std::size_t const n) 
	{ 
		if (n > t_capacity) 
			throw std::bad_alloc(); 

		return buf;
	} 

	void deallocate(T *, std::size_t) 
	{ 
		/* Do Nothing */ 
	} 
}; 

template<typename T, std::size_t t_capacity, std::size_t t_counter, int 
*t_file>
T StaticAllocator<T, t_capacity, t_counter, t_file>::buf[t_capacity]; 

using std::size_t;

#include <vector>
using std::vector;

#include <iostream> 
using std::cout; 
using std::endl; 

auto main(void) -> int 
{
	vector< char, StaticAllocator< char, 4, __COUNTER__ > > v;

	v.push_back('a'); 
	v.push_back('b'); 
	v.push_back('c'); 
	v.push_back('d'); 

	for (auto const &elem : v) 
		cout << elem << endl;

	vector< char, StaticAllocator< char, 4, __COUNTER__ > > v2;

	v2.push_back('x'); 
	v2.push_back('y'); 
	v2.push_back('z');

	for (auto const &elem : v2)
		cout << elem << endl;

	// Now try the first vector again

	for (auto const &elem : v) 
		cout << elem << endl;
}

The trick I'm using with "this_translation_unit" compiles just fine on GNU 
and Clang, however it fails on Microsoft because the variable has internal 
linkage. I'm sure this can be done another way using Boost preprocessor 
stuff. The preprocessor macro "__COUNTER__" is available on every C++ 
compiler I know of.

Frederick

P.S. This is my second idea to the Boost development list. My first one is 
"istream_iterator_limited".

[boost] New allocator that uses global memory

Frederick Gotham