std::assume_aligned
<memory>
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
.
N
must be 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
.
Contents
[edit] Return value
ptr.
[edit] Exceptions
Throws nothing.
[edit] 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 | Value | Std | Feature |
---|---|---|---|
__cpp_lib_assume_aligned |
201811L |
(C++20) | std::assume_aligned
|
[edit] Example
Reason: no example
[edit] See also
alignas
(C++11)
specifies that the storage for the variable should be aligned by specific amount(specifier)[edit]
(class template) [edit]