#include <iostream>
#include <cassert>
using namespace std;
 
class Foo
{
public:
	Foo()
	{
		cout << "construct" << endl;
	}
	~Foo()
	{
		cout << "destruct" << endl;
	}
};
 
Foo* user(void* mem)
{
	cout << " create" << endl;
	return new(mem) Foo();
}
 
int main() {
 
	void* mem=alloca(sizeof(Foo));
	assert(mem);
	Foo* foo=user(mem);
	cerr << "delete" << endl;
	foo->~Foo(); // нужно ЯВНО вызвать деструктор
	//а вот память, выделенную alloca, освобождать НЕ НУЖНО.
	return 0;
}

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