Storing Heterogeneous Objects in C Containers

C containers typically require homogeneous elements, meaning they can only hold objects of a single type. However, there are situations where you may need a container that can accommodate a mix of data types. This article explores how to achieve this using the boost::any library and a custom approach.

Using boost::any

boost::any is a template class that can hold any C type. By storing instances of boost::any in a container, you can have a heterogeneous collection of objects. This approach is recommended for its robustness and handling of edge cases.

Custom Implementation

If you prefer a more manual approach, you can create a custom structure or union that combines members of all expected types along with an indicator to specify the active type.

Structure Approach:

struct HeterogeneousContainer {
  int i;
  std::string s;
  double d;
  int type; // 0 for int, 1 for string, 2 for double
};

Union Approach (use with caution):

union HeterogeneousContainer {
  int i;
  std::string s;
  double d;
};

However, this approach has limitations and potential pitfalls, such as:

• Unions allow only one active member at a time.
• Reading an inactive member may result in undefined behavior.
• Careful handling is required to ensure the correct type is specified and accessed.

Conclusion

When facing the need to store heterogeneous objects in a C container, consider using the boost::any library for its safety and effectiveness. If desired, a custom implementation can be created using a structure or union, but be mindful of their limitations.