DevelopersVoice.com

Q: What are the differences between constant objects?

A: To make any object constant, one uses the keyword 'const'. However, depending on the actual place you insert this keyword, it can have different meanings for the associated object:

1. Reference to object -> Can change the referenced object
   
   foo instance;
   foo& reference_to_instance = instance;
2. Reference to constant object -> Can not change the referenced object
   
   foo instance;
   const foo& constant_reference_to_instance = instance;
3. Pointer to object -> Can change the adress it is pointing to as well as the object
   
   foo instance;
   foo* pointer_to_instance = &instance;
4. Pointer to constant object -> Can change the adress it is pointing to but not the object
   
   foo instance;
   const foo* pointer_to_constant_instance = &instance;
5. Constant pointer -> Can change the object but no the address it is pointing to
   
   foo instance;
   foo* const constant_pointer_to_instance = &instance;
6. Constant pointer to constant object -> Can neither change the address nor the object
   
   foo instance;
   const foo* const constant_pointer_to_constant_instance = &instance;

Note: Most of the material in this article is taken from codeguru.com