17 Language support library [support]

17.6.1 Header <new> synopsis [new.syn]

namespace std {
  // [alloc.errors], storage allocation errors
  class bad_alloc;
  class bad_array_new_length;

  struct destroying_delete_t {
    explicit destroying_delete_t() = default;
  };
  inline constexpr destroying_delete_t destroying_delete{};

  // global operator new control
  \indexlibraryglobal{align_val_t}%
  \indexlibraryglobal{destroying_delete_t}%
  \indexlibraryglobal{destroying_delete}%
  \indexlibraryglobal{nothrow_t}%
  \indexlibraryglobal{nothrow}
  enum class align_val_t : size_t {};

  struct nothrow_t { explicit nothrow_t() = default; };
  extern const nothrow_t nothrow;

  using new_handler = void (*)();
  new_handler get_new_handler() noexcept;
  new_handler set_new_handler(new_handler new_p) noexcept;

  // [ptr.launder], pointer optimization barrier
  template<class T> [[nodiscard]] constexpr T* launder(T* p) noexcept;

  // [hardware.interference], hardware interference size
  inline constexpr size_t hardware_destructive_interference_size = implementation-defined;
  inline constexpr size_t hardware_constructive_interference_size = implementation-defined;
}

// [new.delete], storage allocation and deallocation
[[nodiscard]] void* operator new(std::size_t size);
[[nodiscard]] void* operator new(std::size_t size, std::align_val_t alignment);
[[nodiscard]] void* operator new(std::size_t size, const std::nothrow_t&) noexcept;
[[nodiscard]] void* operator new(std::size_t size, std::align_val_t alignment,
                                 const std::nothrow_t&) noexcept;

void  operator delete(void* ptr) noexcept;
void  operator delete(void* ptr, std::size_t size) noexcept;
void  operator delete(void* ptr, std::align_val_t alignment) noexcept;
void  operator delete(void* ptr, std::size_t size, std::align_val_t alignment) noexcept;
void  operator delete(void* ptr, const std::nothrow_t&) noexcept;
void  operator delete(void* ptr, std::align_val_t alignment, const std::nothrow_t&) noexcept;

[[nodiscard]] void* operator new[](std::size_t size);
[[nodiscard]] void* operator new[](std::size_t size, std::align_val_t alignment);
[[nodiscard]] void* operator new[](std::size_t size, const std::nothrow_t&) noexcept;
[[nodiscard]] void* operator new[](std::size_t size, std::align_val_t alignment,
                                   const std::nothrow_t&) noexcept;

void  operator delete[](void* ptr) noexcept;
void  operator delete[](void* ptr, std::size_t size) noexcept;
void  operator delete[](void* ptr, std::align_val_t alignment) noexcept;
void  operator delete[](void* ptr, std::size_t size, std::align_val_t alignment) noexcept;
void  operator delete[](void* ptr, const std::nothrow_t&) noexcept;
void  operator delete[](void* ptr, std::align_val_t alignment, const std::nothrow_t&) noexcept;

[[nodiscard]] void* operator new  (std::size_t size, void* ptr) noexcept;
[[nodiscard]] void* operator new[](std::size_t size, void* ptr) noexcept;
void  operator delete  (void* ptr, void*) noexcept;
void  operator delete[](void* ptr, void*) noexcept;

17.6.2 Storage allocation and deallocation [new.delete]

T* p1 = new T;                  // throws bad_­alloc if it fails
T* p2 = new(nothrow) T;         // returns nullptr if it fails

void* place = operator new(sizeof(Something));
Something* p = new (place) Something();

17.6.3 Storage allocation errors [alloc.errors]

namespace std {
  class bad_alloc : public exception {
  public:
    // see [exception] for the specification of the special member functions
    const char* what() const noexcept override;
  };
}

namespace std {
  class bad_array_new_length : public bad_alloc {
  public:
    // see [exception] for the specification of the special member functions
    const char* what() const noexcept override;
  };
}

17.6.4 Pointer optimization barrier [ptr.launder]

struct X { int n; };
const X *p = new const X{3};
const int a = p->n;
new (const_cast<X*>(p)) const X{5}; // p does not point to new object ([basic.life]) because its type is const
const int b = p->n;                 // undefined behavior
const int c = std::launder(p)->n;   // OK

17.6.5 Hardware interference size [hardware.interference]

struct keep_apart {
  alignas(hardware_destructive_interference_size) atomic<int> cat;
  alignas(hardware_destructive_interference_size) atomic<int> dog;
};

struct together {
  atomic<int> dog;
  int puppy;
};
struct kennel {
  // Other data members...
  alignas(sizeof(together)) together pack;
  // Other data members...
};
static_assert(sizeof(together) <= hardware_constructive_interference_size);