C++ Memory Management: What are the differences between constant objects?

[Andreas Masur]

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:

• Reference to object -> Can change the referenced object
  
  

  foo instance;
  foo& reference_to_instance = instance;

• Reference to constant object -> Can not change the referenced object
  
  

  foo instance;
  const foo& constant_reference_to_instance = instance;

• Pointer to object -> Can change the adress it is pointing to as well as the object
  
  

  foo instance;
  foo* pointer_to_instance = &instance;

• 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;

• Constant pointer -> Can change the object but no the address it is pointing to
  
  

  foo instance;
  foo* const constant_pointer_to_instance = &instance;

• Constant pointer to constant object -> Can neither change the address nor the object
  
  

  foo instance;
  const foo* const constant_pointer_to_constant_instance = &instance;