| Home | Libraries | People | FAQ | More

## Rationale

#### Dynamic allocation

C++11 added the ability to specify increased alignment (over-alignment) for class types. Unfortunately, `::operator new` allocation functions, `new` expressions, and the default allocator, `std::allocator`, do not support dynamic memory allocation of over-aligned data. This library provides allocation functions, allocators, allocator adaptors, and deleters, that are alignment aware.

Table 2.2. Boost.Align solutions

Problem | Solution
--- | ---
`::operator new(std::size_t, const std::no_throw_t&)` | `aligned_alloc(std::size_t, std::size_t)`
`::operator delete(void*)` | `aligned_free(void*)`
`std::allocator<T>` | `aligned_allocator<T>`
`Allocator` | `aligned_allocator_adaptor<Allocator>`
`std::default_delete<T>` | `aligned_delete`

#### Alignment functions

C++11 provided `std::align` in the standard library to align a pointer value. Unfortunately some C++ standard library implementations do not support it yet (libstdc++ as far as gcc 4.8.0) and other standard library implementations implement it incorrectly (dinkumware in msvc 11.0). This library provides it for those implementations and also for C++03 compilers where it is equally useful.

#### Alignment traits

C++11 provided the `std::alignment_of` trait in the standard library to query the alignment requirement of a type. Unfortunately some C++ standard library vendors do not implement it in an entirely standard conforming manner, such as for array types (libc++ as far as clang 3.4). Other vendor implementations report incorrect values for certain types, such as pointer to members (msvc 14.0). This library provides it for those implementations and also for C++03 compilers where it is equally useful.

#### Alignment hints

Allocating aligned memory is sometimes not enough to ensure that optimal code is generated. Developers use specific compiler intrinsics to notify the compiler of a given alignment property of a memory block. This library provides a macro to abstract that functionality for compilers with the appropriate intrinsics.

#### Alignment testing

This library provides a function to test the alignment of a pointer value. It is generally useful in assertions to validate that memory is correctly aligned.