Question

I am programming in C++ more then 5 years, and have never met any place where reference of the variable is recommended to use except as a function argument (if you don’t want to copy what you pass as your function argument). So could someone point cases where C++ variable reference is recommended (I mean it gives any advantage) to use.

Answer 1

As a return value of an opaque collection accessor/mutator

The operator[] of std::map returns a reference.

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To shorten the text needed to reference a variable

If you miss old-school with Foo do ... statement (that’s Pascal syntax), you can write

 MyString &name = a->very->long_->accessor->to->member;
 if (name.upcase() == "JOHN") {
    name += " Smith";
 }

another example of this can be found in Mike Dunlavey’s answer

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To state that something is just a reference

References are also useful in wrapper objects and functors–i.e. in intermediate objects that logically contact no members but only references to them.

Example:

class User_Filter{
  std::list<User> const& stop_list;
  public: Functor (std::list<User> const& lst)
    : stop_list(lst) { }
  public: bool operator()(User const& u) const
    {  return stop_list.exists(u); }
};

find_if(x.begin(),x.end(),User_Filter(user_list));

The idea here that it’s a compile error if you don’t initialize a reference in constructor of such an object. The more checks in compile time–the better programs are.