Question

While implementing a FIFO I have used the following structure:

struct Node
{
    T info_;
    Node* link_;
    Node(T info, Node* link=0): info_(info), link_(link)
    {}
};

I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it’s pointer? Is this a kind of infinite loop?

And finally, if this is a bad practice, how I could implement a better FIFO.

EDIT: People, this is all about implemenation. I am enough familiar with STL library, and know a plenty of containers from several libraries. Just I want to discuss with people who can gave a good implementation or a good advice.

Answer 1

Pointers to objects of type that is being declared is fine in both C and C++. This is based on the fact that pointers are objects of fixed size (say, always 32-bit integers on 32-bit platform) so you don’t need the full size of the pointed-to type to be known.

In fact, you don’t even need a full type declaration to declare a pointer. A forward declaration would suffice:

class A; // forward declared type

struct B
{
    A* pa; //< pointer to A - perfectly legal
};

Of course, you need a full declaration in scope at the point where you actually access members:

#include <A.hpp> // bring in full declaration of class A
...
B b;
b.pa = &a; // address of some instance of A
...
b.pa->func(); // invoke A's member function - this needs full declaration

For FIFO look into std::queue. Both std::list, std::deque, and std::vector could be used for that purpose, but also provide other facilities.