C++11 provides standardized methods for specifying and querying the alignment requirements of a type (something that was previously possible only through compiler-specific methods). Controlling the alignment is important in order to boost performance on different processors and enable the use of some instructions that only work with data on particular alignments. For example, Intel SSE and Intel SSE2 require 16 bytes alignment of data, whereas for Intel Advanced Vector Extensions (or Intel AVX), it is highly recommended to use 32 bytes alignment. This recipe explores the alignas specifier for controlling the alignment requirements and the alignof operator that retrieves the alignment requirements of a type.
You should be familiar with what data alignment is and the way the compiler performs default data alignment. However, basic information about the latter is provided in the How it works... section.