An allocation function shall be a class member function or a global
function; a program is ill-formed if an allocation function is declared
in a namespace scope other than global scope or declared static in
global scope.
The first
parameter shall have type std::size_t ([support.types]).
The
first parameter shall not have an associated default
argument ([dcl.fct.default]).
The value of the first parameter
is interpreted as the requested size of the allocation.
An allocation
function can be a function template.
Such a template shall declare its
return type and first parameter as specified above (that is, template
parameter types shall not be used in the return type and first parameter
type).
Template allocation functions shall have two or more parameters.
An allocation function attempts to allocate the requested amount of
storage.
If it is successful, it returns the address of the start
of a block of storage whose length in bytes is at least as large
as the requested size.
The order,
contiguity, and initial value of storage allocated by successive calls
to an allocation function are unspecified.
Even if the size of the space
requested is zero, the request can fail.
If the request succeeds, the
value returned by a replaceable allocation function
is a non-null pointer value ([basic.compound])
p0 different from any previously returned value p1,
unless that value p1 was subsequently passed to a
replaceable deallocation function.
Furthermore, for the library allocation functions
in [new.delete.single] and [new.delete.array],
p0 represents the address of a block of storage disjoint from the storage
for any other object accessible to the caller.
The effect of indirecting through a pointer
returned from a request for zero size is undefined.32
For an allocation function other than
a reserved placement allocation function ([new.delete.placement]),
the pointer returned on a successful call
shall represent the address of storage that is aligned as follows:
If the allocation function takes an argument
of type std::align_val_t,
the storage will have the alignment specified
by the value of this argument.
Otherwise, if the allocation function is named operatornew[],
the storage is aligned for any object that
does not have new-extended alignment ([basic.align]) and
is no larger than the requested size.
A program-supplied allocation function can obtain the address of the
currently installed new_handler using the
std::get_new_handler function ([get.new.handler]).
— end note
]
An allocation function that has a non-throwing
exception specification ([except.spec])
indicates failure by returning
a null pointer value.
Any other allocation function
never returns a null pointer value and
indicates failure only by throwing an exception ([except.throw]) of a type
that would match a handler ([except.handle]) of type
std::bad_alloc ([bad.alloc]).
A global allocation function is only called as the result of a new
expression, or called directly using the function call
syntax, or called indirectly to allocate storage for
a coroutine state ([dcl.fct.def.coroutine]),
or called indirectly through calls to the
functions in the C++ standard library.