Circular dependent structs in C/C++

Question

Heres a simple question, I'm implementing suffix array but I'm stuck here:

#define SIZE 150

struct node{
     transition *next[SIZE];   //error here
};

struct transition{
    int left, right;
    node *suffix_link;
};

This code won't compile, there's an error in the third line, can anyone help me plz? thanks :D

UPDATE: My bad I forgot to include the first line, sorry it's my first question here :P

What's the error? You could try moving the definition/declaration of `transition` before `node`. — wkl, Mar 29 '12 at 20:49
@birryree that would still give an error, because `node` wouldn't be declared for transition, and you'd still need a forward declaration. — Luchian Grigore, Mar 29 '12 at 20:52
@LuchianGrigore - oh good point - I didn't notice that they were circularly dependent. — wkl, Mar 29 '12 at 20:52
@birryree: Notice that `node` and `transition` have a circular dependency. — Frank, Mar 29 '12 at 20:53

score 8 · Answer 1 · answered Mar 29 '12 at 20:49

8

You need to forward declare transition:

struct transition;  // <-- forward declaration

struct node{
     transition *next[SIZE];
};

struct transition{
    int left, right;
    node *suffix_link;
};

answered Mar 29 '12 at 20:49

Luchian Grigore

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score 1 · Answer 2 · answered Mar 29 '12 at 20:51

1

Use a forward declaration:

struct transition;

struct node
{
    transition *next[SIZE];
};

struct transition
{
   int left, right;
   node *suffix_link;
};

answered Mar 29 '12 at 20:51

Frank

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score 1 · Answer 3 · answered Mar 29 '12 at 20:55

1

Why forward declaration?

Because, the complete defintion of transition is not yet known to the compiler when you use it.

The same is not required for node because it's already been defined when you use it in transition.

answered Mar 29 '12 at 20:55

P.P

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Circular dependent structs in C/C++

3 Answers3