only_on_stack type

onlystack.cpp

#include <iostream>
#include <stdexcept>

#if _MSC_VER
#define NO_INLINE __declspec(noinline)
#else
#define NO_INLINE __attribute__ ((noinline))
#endif

struct stack_marker
{
	thread_local static uint8_t* marker;
	uint8_t stk;

	stack_marker()
	{
		if (marker != nullptr)
		{
			throw std::runtime_error("second twice marker! don't do it");
		}
		marker = &stk;
	}
};

thread_local uint8_t* stack_marker::marker = nullptr;

void sort3(uint8_t* (&a)[3])
{
	if (a[0] > a[1])
	    std::swap(a[0], a[1]);
	if (a[0] > a[2])
	    std::swap(a[0], a[2]);
	if (a[1] > a[2])
	    std::swap(a[1], a[2]);
}

class only_on_stack
{
	uint8_t place;
public:
	NO_INLINE only_on_stack(int x)
	{
		uint8_t a;

		if (!stack_marker::marker)
		{
			// not initialized yet, either forgot to put stack_marker in main
			// or we are running before main, which is static storage

			//throw std::runtime_error("only on stack object created in non-stack");
			std::cout << x << ": I'm NOT on stack\n";
		    return;
		}

		uint8_t* ptrs[] = {
			stack_marker::marker,
			&place,
			&a
		};

		sort3(ptrs);

		if (ptrs[1] == &place) // place must be in the middle
		{
			std::cout << x << ": I'm on stack\n";
		}
		else
		{
			//throw std::runtime_error("only_on_stack object created in non-stack");
			std::cout << x << ": I'm NOT on stack\n";
		}
	}
};

only_on_stack static_storage(1);
thread_local only_on_stack tl_storage(4);

int NO_INLINE stuff()
{
	only_on_stack oos(2);
	only_on_stack test(5);
}

int main()
{
	stack_marker mrk;
	stuff();
	auto test = new only_on_stack(3);
	tl_storage; // access thread local to construct
}