C++ Structure within itself?

Question

I've been trying to port this code to python, but there is something I do not quite understand in C++ (I do know a bit of C++ but this is beyond me):

typedef struct huffnode_s
{
    struct huffnode_s *zero;
    struct huffnode_s *one;
    unsigned char val;
    float freq;
} huffnode_t;

What I don't get is how huffnode_s can be within itself, I've never seen this before and don't quite understand it. What does this mean, and if someone can, what would be the python equivalent?

Answer 1

huffnode_s isn't within itself, only pointers to huffnode_s are in there. Since a pointer is of known size, it's no problem.

Answer 2

This.

class Huffnode(object):
    def __init__(self, zero, one, val, freq):
        """zero and one are Huffnode's, val is a 'char' and freq is a float."""
        self.zero = zero
        self.one = one
        self.val = val
        self.freq = freq

You can then refactor your various C functions to be methods of this class.

Or maybe this.

from collections import namedtuple
Huffnode = namedtuple( 'Huffnode', [ 'zero', 'one', 'val', 'freq' ] )

If you want your C functions to remain functions.

That's it.

h0 = Huffnode(None, None, 'x', 0.0)
h1 = Huffnode(None, None, 'y', 1.0)
h2 = Huffnode(h0, h1, 'z', 2.0)

That's all that's required.

Answer 3

it does not have a structure in itself. it has a pointer to that structure.

in memory struct huffnode_s would look like (32 bit machine):

---

|------------------ huffnode_s* zero - 4 bytes --------------|

|------------------ huffnode_s* one - 4 bytes----------------|

|unsigned char val - 1 byte + 3 bytes padding=======|

|------------------- float freq - 4 bytes -------------------------|

---

these sizes would vary machine to machine, and how it looks in memory is decided by compiler .