How to Determine if a Type is an STL Container at Compile Time in C ?

Determining STL Container Types at Compile Time

In this article, we explore a common requirement in C : determining whether a given type represents an STL container at compile time. An STL container is a data structure that conforms to a specific set of requirements, such as having begin() and end() iterators.

The Problem

The question arises from a need to have a template that can identify if a given type is an STL container. However, the provided code lacks the necessary specializations to handle specific STL containers like std::vector, std::deque, std::set, etc.

The Solution

To address this, we present a comprehensive solution:

is_container Class Template

This class template uses specific traits to determine if a type meets the criteria of an STL container:

template<typename T> 
struct is_container : std::integral_constant<bool, has_const_iterator<T>::value && has_begin_end<T>::beg_value && has_begin_end<T>::end_value> 
{ };

• has_const_iterator checks if the type has a const_iterator type.
• has_begin_end checks if the type has begin() and end() member functions that return iterators.

Usage

Using is_container is straightforward. Pass the type to the template and evaluate its value:

std::cout << is_container<std::vector<int>>::value << std::endl; // true
std::cout << is_container<int>::value << std::endl; // false

Helper Trait Classes

The is_container class template relies on the following helper trait classes:

• has_const_iterator determines if the type has a const_iterator type.
• has_begin_end checks if the type has begin() and end() member functions that return iterators.

Conclusion

This technique provides a concise and reliable method for determining whether a type represents an STL container at compile time, enabling flexible and type-safe code manipulation.

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