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It is acceptable to define a deleted allocation or deallocation function without its corresponding free store function. For instance, it is a common practice to define a deleted non-placement allocation or deallocation function as a class member function when the class also defines a placement new function. This prevents accidental allocation via calls to new for that class type , or deallocation via calls to delete on pointers to an object of that class type. It is acceptable to declare, but not define, a private allocation or deallocation function without its corresponding free store function for similar reasons. However, a definition must not be provided as that still allows access to the free store function within a class member function.
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In this compliant solution, the corresponding deallocation function is also defined at global scope:.
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#include <Windows.h>
#include <new>
class HeapAllocator {
static HANDLE h;
static bool init;
public:
static void *alloc(std::size_t size) noexcept(false) {
if (!init) {
h = ::HeapCreate(0, 0, 0); // Private, expandable heap.
init = true;
}
if (h) {
return ::HeapAlloc(h, 0, size);
}
throw std::bad_alloc();
}
static void dealloc(void *ptr) noexcept {
if (h) {
(void)::HeapFree(h, 0, ptr);
}
}
};
HANDLE HeapAllocator::h = nullptr;
bool HeapAllocator::init = false;
void *operator new(std::size_t size) noexcept(false) {
return HeapAllocator::alloc(size);
}
void operator delete(void *ptr) noexcept {
return HeapAllocator::dealloc(ptr);
} |
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In this compliant solution, the corresponding operator delete() is overloaded at the same class scope:.
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#include <new>
extern "C++" void update_bookkeeping(void *allocated_ptr, std::size_t size, bool alloc);
struct S {
void *operator new(std::size_t size) noexcept(false) {
void *ptr = ::operator new(size);
update_bookkeeping(ptr, size, true);
return ptr;
}
void operator delete(void *ptr, std::size_t size) noexcept {
::operator delete(ptr);
update_bookkeeping(ptr, size, false);
}
}; |
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