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Difference between ‘struct’ and ‘typedef struct’ in C++?

An answer to this question led me to wonder about the following:

I presume that defining a class as follows:

typedef class {int i;} C;

would be completely equivalent to defining it in the conventional manner:

class C
{
   int i;
};

Is this presumption correct?

Answer 1

In this isolated example they are functionally the same, at least from the outside.

However there are differences. One instance in particular, you cannot declare a constructor for a struct or a class declared in this way, simply because the class is unnamed. Similarly you cannot declare any function that involves the class’ name. Here are some examples:

typedef class
{
public:
  Gizmo() : n_(42) {}; // NOT OK
  ~Gizmo();
  Gizmo& operator<<(int n);    
private:
  int n_;
} Gizmo;

You also cannot forward declare an anonymous class:

class Gizmo;

In C++ I have never seen a case where typedefing an anonymous struct or a class is preferable to simply declaring a class or a struct that is named. In some cases the traditional method is definitely preferred. The moral of the story is: don’t use typedef class {} Name; in C++. It buys you nothing, and costs you something.