table of contents
std::assume_aligned(3) | C++ Standard Libary | std::assume_aligned(3) |
NAME¶
std::assume_aligned - std::assume_aligned
Synopsis¶
Defined in header <memory>
template< std::size_t N, class T > (since C++20)
[[nodiscard]] constexpr T* assume_aligned(T* ptr);
Informs the implementation that the object ptr points to is aligned to at
least N.
The implementation may use this information to generate more efficient code,
but it
might only make this assumption if the object is accessed via the return
value of
assume_aligned.
The program is ill-formed if N is not a power of 2. The behavior is undefined
if ptr
does not point to an object of type T (ignoring cv-qualification at every
level), or
if the object's alignment is not at least N.
Return value¶
ptr.
Exceptions¶
Throws nothing.
Notes¶
To ensure that the program benefits from the optimizations
enabled by
assume_aligned, it is important to access the object via its return
value:
void f(int* p) {
int* p1 = std::assume_aligned<256>(p);
// Use p1, not p, to ensure benefit from the alignment assumption.
// However, the program has undefined behavior if p is not aligned
// regardless of whether p1 is used.
}
It is up to the program to ensure that the alignment assumption actually
holds. A
call to assume_aligned does not cause the compiler to verify or enforce
this.
Feature-test macro: __cpp_lib_assume_aligned
See also¶
alignof operator(C++11) queries alignment requirements of
a type
alignas specifier(C++11) specifies that the storage for the variable
should be
aligned by specific amount
aligned_storage defines the type suitable for use as uninitialized
(C++11)(deprecated in C++23) storage for types of given size
(class template)
align aligns a pointer in a buffer
(C++11) (function)
2022.07.31 | http://cppreference.com |