std::assume_aligned
Defined in header <memory>
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template< std::size_t N, class T > [[nodiscard]] constexpr T* assume_aligned(T* ptr); |
(since C++20) | |
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.