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Showing content from https://timsong-cpp.github.io/cppwp/n4140/new.delete below:

18 Language support library [language.support]

18.6.1.1 Single-object forms [new.delete.single]

void* operator new(std::size_t size);

Replaceable: a C++ program may define a function with this function signature that displaces the default version defined by the C++ standard library.

Required behavior: Return a non-null pointer to suitably aligned storage ([basic.stc.dynamic]), or else throw a bad_alloc exception. This requirement is binding on a replacement version of this function.

Default behavior:

void* operator new(std::size_t size, const std::nothrow_t&) noexcept;

Effects: Same as above, except that it is called by a placement version of a new-expression when a C++ program prefers a null pointer result as an error indication, instead of a bad_alloc exception.

Replaceable: a C++ program may define a function with this function signature that displaces the default version defined by the C++ standard library.

Required behavior: Return a non-null pointer to suitably aligned storage ([basic.stc.dynamic]), or else return a null pointer. This nothrow version of operator new returns a pointer obtained as if acquired from the (possibly replaced) ordinary version. This requirement is binding on a replacement version of this function.

Default behavior: Calls operator new(size). If the call returns normally, returns the result of that call. Otherwise, returns a null pointer.

Example:

T* p1 = new T;                  T* p2 = new(nothrow) T;         

 — end example ]

void operator delete(void* ptr) noexcept; void operator delete(void* ptr, std::size_t size) noexcept;

Replaceable: a C++ program may define a function with signature void operator delete(void* ptr) noexcept that displaces the default version defined by the C++ standard library. If this function (without size parameter) is defined, the program should also define void operator delete(void* ptr, std::size_t size) noexcept. If this function with size parameter is defined, the program shall also define the version without the size parameter. [ Note: The default behavior below may change in the future, which will require replacing both deallocation functions when replacing the allocation function.  — end note ]

Requires: ptr shall be a null pointer or its value shall be a value returned by an earlier call to the (possibly replaced) operator new(std::size_t) or operator new(std::size_t,const std::nothrow_t&) which has not been invalidated by an intervening call to operator delete(void*).

Requires: If present, the std::size_t size argument shall equal the size argument passed to the allocation function that returned ptr.

Required behavior: Calls to operator delete(void* ptr, std::size_t size) may be changed to calls to operator delete(void* ptr) without affecting memory allocation. [ Note: A conforming implementation is for operator delete(void* ptr, std::size_t size) to simply call operator delete(ptr).  — end note ]

Default behavior: the function operator delete(void* ptr, std::size_t size) calls operator delete(ptr). [ Note: See the note in the above Replaceable paragraph.  — end note ]

Default behavior: If ptr is null, does nothing. Otherwise, reclaims the storage allocated by the earlier call to operator new.

Remarks: It is unspecified under what conditions part or all of such reclaimed storage will be allocated by subsequent calls to operator new or any of calloc, malloc, or realloc, declared in <cstdlib>.

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

Replaceable: a C++ program may define a function with signature void operator delete(void* ptr, const std::nothrow_t&) noexcept that displaces the default version defined by the C++ standard library. If this function (without size parameter) is defined, the program should also define void operator delete(void* ptr, std::size_t size, const std::nothrow_t&) noexcept. If this function with size parameter is defined, the program shall also define the version without the size parameter. [ Note: The default behavior below may change in the future, which will require replacing both deallocation functions when replacing the allocation function.  — end note ]

Requires: If present, the std::size_t size argument must equal the size argument passed to the allocation function that returned ptr.

Required behavior: Calls to operator delete(void* ptr, std::size_t size, const std::nothrow_t&) may be changed to calls to operator delete(void* ptr, const std::nothrow_t&) without affecting memory allocation. [ Note: A conforming implementation is for operator delete(void* ptr, std::size_t size, const std::nothrow_t&) to simply call operator delete(void* ptr, const std::nothrow_t&).  — end note ]

Default behavior: operator delete(void* ptr, std::size_t size, const std::nothrow_t&) calls operator delete(ptr, std::nothrow), and operator delete(void* ptr, const std::nothrow_t&) calls operator delete(ptr).

18.6.1.2 Array forms [new.delete.array]

void* operator new[](std::size_t size);

Replaceable: a C++ program can define a function with this function signature that displaces the default version defined by the C++ standard library.

Required behavior: Same as for operator new(std::size_t). This requirement is binding on a replacement version of this function.

Default behavior: Returns operator new(size).

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

Effects: Same as above, except that it is called by a placement version of a new-expression when a C++ program prefers a null pointer result as an error indication, instead of a bad_alloc exception.

Replaceable: a C++ program can define a function with this function signature that displaces the default version defined by the C++ standard library.

Required behavior: Return a non-null pointer to suitably aligned storage ([basic.stc.dynamic]), or return a null pointer. This requirement is binding on a replacement version of this function.

Default behavior: Calls operator new[](size). If the call returns normally, returns the result of that call. Otherwise, returns a null pointer.

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

Replaceable: a C++ program can define a function with signature void operator delete[](void* ptr) noexcept that displaces the default version defined by the C++ standard library. If this function (without size parameter) is defined, the program should also define void operator delete[](void* ptr, std::size_t size) noexcept. If this function with size parameter is defined, the program shall also define the version without the size parameter. [ Note: The default behavior below may change in the future, which will require replacing both deallocation functions when replacing the allocation function.  — end note ]

Requires: ptr shall be a null pointer or its value shall be the value returned by an earlier call to operator new[](std::size_t) or operator new[](std::size_t,const std::nothrow_t&) which has not been invalidated by an intervening call to operator delete[](void*).

Requires: If present, the std::size_t size argument must equal the size argument passed to the allocation function that returned ptr.

Required behavior: Calls to operator delete[](void* ptr, std::size_t size) may be changed to calls to operator delete[](void* ptr) without affecting memory allocation. [ Note: A conforming implementation is for operator delete[](void* ptr, std::size_t size) to simply call operator delete[](void* ptr).  — end note ]

Default behavior: operator delete[](void* ptr, std::size_t size) calls operator delete[](ptr), and operator delete[](void* ptr) calls operator delete(ptr).

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

Replaceable: a C++ program may define a function with signature void operator delete[](void* ptr, const std::nothrow_t&) noexcept that displaces the default version defined by the C++ standard library. If this function (without size parameter) is defined, the program should also define void operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) noexcept. If this function with size parameter is defined, the program shall also define the version without the size parameter. [ Note: The default behavior below may change in the future, which will require replacing both deallocation functions when replacing the allocation function.  — end note ]

Requires: If present, the std::size_t size argument must equal the size argument passed to the allocation function that returned ptr.

Required behavior: Calls to operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) may be changed to calls to operator delete[](void* ptr, const std::nothrow_t&) without affecting memory allocation. [ Note: A conforming implementation is for operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) to simply call operator delete[](void* ptr, const std::nothrow_t&).  — end note ]

Default behavior: operator delete[](void* ptr, std::size_t size, const std::nothrow_t&) calls operator delete[](ptr, std::nothrow), and operator delete[](void* ptr, const std::nothrow_t&) calls operator delete[](ptr).

18.6.1.3 Placement forms [new.delete.placement]

These functions are reserved, a C++ program may not define functions that displace the versions in the Standard C++ library ([constraints]). The provisions of ([basic.stc.dynamic]) do not apply to these reserved placement forms of operator new and operator delete.

void* operator new(std::size_t size, void* ptr) noexcept;

Remarks: Intentionally performs no other action.

Example: This can be useful for constructing an object at a known address:

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

 — end example ]

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

Remarks: Intentionally performs no other action.

void operator delete(void* ptr, void*) noexcept;

Effects: Intentionally performs no action.

Remarks: Default function called when any part of the initialization in a placement new expression that invokes the library's non-array placement operator new terminates by throwing an exception ([expr.new]).

void operator delete[](void* ptr, void*) noexcept;

Effects: Intentionally performs no action.

Remarks: Default function called when any part of the initialization in a placement new expression that invokes the library's array placement operator new terminates by throwing an exception ([expr.new]).


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