const CFoo &bar() const

I have a property of a class, for example, const C开发者_运维技巧Foo &bar() const, what does it mean?

The method bar returns a reference to a const CFoo (that's the const CFoo & part before bar), and calling this method does not modify any variables that are not marked as mutable (that's the const after the parentheses).

See also the C++ FAQ Lite entries What does "Fred const& X" mean? and What is a "const member function"?.

const CFoo& bar() const
----------      --------
      ^               ^
Returns a connst      None of the member variables of the class to which bar
reference of CFoo.    method belongs to can be modified.
                      unless member variable is prefexex with keyword mutable

It's a const function (doesn't modify any non-mutable members of the object) member function that returns a reference to a const CFoo.