Pointers in struct to itself

Dominik Reichl

Hi! I want to define a structure that has 2 pointers to the same type as itself. For example, think of a Huffman tree node. In C++ we did it like this:

typedef struct
{
unsigned int code;
unsigned int count;
HUFFTREENODE *l;
HUFFTREENODE *r;
} HUFFTREENODE;

Now, how can we do the same in C#? I tried this:

public struct HuffTreeNode
{
uint code;
uint count;
HuffTreeNode l;
HuffTreeNode r;
}

But it gives me an error that this would create a loop in the struct... Thanks in advance and best regards Dominik

_outp(0x64, 0xAD); and __asm mov al, 0xAD __asm out 0x64, al do the same... but what do they do?? ;) (doesn't work on NT)

Mathew Hall

You'd probably want to do something like:

[StructLayout(LayoutKind.Sequential)]
public struct HuffTreeNode
{
uint code;
uint count;
IntPtr leftNode;
IntPtr rightNode;
}

and then use Marshal.StructureToPtr[^] and Marshal.PtrToStructure[^] to convert the struct to/from a pointer "I think I speak on behalf of everyone here when I say huh?" - Buffy

Dominik Reichl

Thanks! Interestingly, when I replace 'struct' by 'class', the code I posted first compiles nicely (why??)... What do you think is more efficient? Making the thingy a class or leaving it as struct and using Marshal.etc? I won't have that many nodes, only about 66000... Thanks again and best regards Dominik

_outp(0x64, 0xAD); and __asm mov al, 0xAD __asm out 0x64, al do the same... but what do they do?? ;) (doesn't work on NT)

Daniel Turini

Dominik Reichl wrote: What do you think is more efficient? Making the thingy a class or leaving it as struct and using Marshal.etc? I won't have that many nodes, only about 66000... Structs should (mostly) only used for Interop calls. As it seems you're designing a Huffman class library, with no interop calls, I'd create it as a class. I don't see dead pixels anymore... Yes, even I am blogging now!

mav northwind

Structs are value types, classes are reference types, that's why it compiles when you use class but not when you use struct. In a class you can easily have a reference to another class (even to itself), but in a struct the compiler would have to allocate space for the contents of the struct. That's why a struct must not contain itself. Regards, mav