[英]C++17 polymorphic memory recources not working
I was trying to understand the c++17 pmr. 我试图了解c ++ 17 pmr。 So I did this and it is not working as I thought, what could go wrong? 所以我这样做了,但它没有按照我的想法工作,可能出什么问题了?
template <typename T>
class Memory : public std::experimental::pmr::memory_resource {
public:
Memory() { this->memory = allocate(sizeof(T), alignof(T)); }
void *getMemory() { return this->memory; }
~Memory() { deallocate(this->memory, sizeof(T), alignof(T)); }
private:
void *do_allocate(std::size_t bytes, std::size_t alignment)
{
memory = ::operator new(bytes);
}
void do_deallocate(void *p, std::size_t bytes, std::size_t alignment)
{
::operator delete(memory);
}
bool do_is_equal(
const std::experimental::pmr::memory_resource& other) const noexcept
{
}
void *memory;
};
what can be going wrong with my implementation? 我的实现有什么问题? This is the client.. 这是客户
Memory<std::string> mem;
std::string * st = (std::string*)mem.getMemory();
st->assign("Pius");
std::cout << *st;
The polymorphic resource allocators allocate memory ; 多态资源分配器分配内存 ; that's all they do. 那就是他们所做的一切。 Unlike container Allocators, they don't create objects . 与容器分配器不同,它们不创建对象 。 That's why they return void*
s. 这就是为什么它们返回void*
的原因。
Memory resources are not meant to be used by themselves. 内存资源并不意味着要自己使用。 That's why std::polymorphic_allocator<T>
exists. 这就是为什么存在std::polymorphic_allocator<T>
的原因。 You can also do the object creation/destruction yourself, using placement- new
and manual destructor calls. 您还可以使用“ placement”( new
和手动的析构函数调用)自行创建/破坏对象。
Also, your memory_resource implementation makes no sense. 同样,您的memory_resource实现没有任何意义。 do_allocate
should return the allocated memory, not store it internally. do_allocate
应该返回分配的内存,而不是在内部存储它。 Your function provokes undefined behavior by returning nothing (which your compiler should have warned about). 您的函数通过不返回任何内容(编译器应该警告过)来引发未定义的行为。
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