Question

I would like to write a template that will determine if a type is an stl container at compile time.  

I’ve got the following bit of code:

struct is_cont{};
struct not_cont{};

template <typename T>
struct is_cont { typedef not_cont result_t; };

but I’m not sure how to create the necessary specializations for std::vector<T,Alloc>, deque<T,Alloc>, set<T,Alloc,Comp> etc…

Answer 1

First, you define your primary template, which will have a member which is false in the default case:

template <typename T>
struct is_cont {
  static const bool value = false;
};

Then you will define partial specializations for your container types which have a value of true instead:

template <typename T,typename Alloc>
struct is_cont<std::vector<T,Alloc> > {
  static const bool value = true;
};

Then for a type X that you want to check, use it like

if (is_cont<X>::value) { ... }