How do you calculate automatic array offsets using variadic templates in C ?

Creating an Array Initializer from a Tuple or Variadic Template Parameters

Variadic templates offer a solution to the need for automatic offset calculation in array initialization. By representing each element as an identifier and its size, a sequence can be created that drives the calculation of offsets.

A Layout structure is employed to hold the entries:

<code class="cpp">template<:size_t offset typename key typename... entries>
struct LayoutHelper {
  typedef std::tuple type;
};
template<typename key typename... entries>
struct Layout:LayoutHelper {};</typename></:size_t></code>

Each entry has an identifier and a type or size:

<code class="cpp">template<typename key identifier typename data>
struct Entry {};</typename></code>

To create a processed entry, we extend the concept:

<code class="cpp">template<:size_t offset typename key id0 d0 typename... entries>
struct LayoutHelper<offset key entry id0 d0>, Entries...>
{
    typedef typename prepend
        
        , typename LayoutHelper<offset key entries...>::type
        > type;
};</offset></offset></:size_t></code>

Usage looks like this:

<code class="cpp">Layout, Entry > layout;</code>

After finding a prepend implementation that adds elements to the front of a tuple, Layout::type will represent a tuple that expresses the data layout. This result can then be used to construct a std::array by unpacking the entries using the indexes technique.

The above is the detailed content of How do you calculate automatic array offsets using variadic templates in C ?. For more information, please follow other related articles on the PHP Chinese website!