C recursive typedef structures

Question

I have the following working code.

#include <stdlib.h>
#include <stdio.h>

typedef struct Mystruct {
    int id;
    struct Mystruct** mystructures;
} Mystruct;

int main () {
    Mystruct* ms1 = malloc(sizeof(Mystruct));
    ms1->id = 1;

    Mystruct* ms2 = malloc(sizeof(Mystruct));
    ms2->id = 2;

    Mystruct* ms3 = malloc(sizeof(Mystruct));
    ms3->id = 3;

    ms1->mystructures = malloc(sizeof(Mystruct) * 2);
    ms1->mystructures[0] = (struct Mystruct*)ms2;
    ms1->mystructures[1] = (struct Mystruct*)ms3;

    printf("%d\n", ms1->mystructures[0]->id);
}

I don't like having to use both Mystruct and (struct Mystruct) to refer to the same data type. Is there a way to use typedefined Mystruct recursively like in

typedef struct {
    int id;
    Mystruct** mystructures;
} Mystruct;

? This doesn't compile. Thanks

I do not like Marmite https://en.wikipedia.org/wiki/Marmite either. So not really a problem — Ed Heal, Aug 02 '15 at 09:10
Well, I was about to post an answer when this was marked as duplicate. Anyway, there's a bug in your code here: `ms1->mystructures = malloc(sizeof(Mystruct) * 2);`. `mystructures` is of type `Mystruct **`, so you need to allocate space for `Mystruct *`. It should be `malloc(sizeof(Mystruct *) * 2);`. — Filipe Gonçalves, Aug 02 '15 at 09:17
To avoid this kind of mistakes, I usually prefer (and recommend) to use `sizeof(*X)` when allocating space for `X`, this makes sure you always allocate the correct amount. So in this case you'd do `malloc(sizeof(*ms1->mystructures) * 2)`. — Filipe Gonçalves, Aug 02 '15 at 09:18

score 1 · Accepted Answer · answered Aug 02 '15 at 09:09

1

First define your typedef and then the struct:

typedef struct Mystruct Mystruct;

struct Mystruct {
    int id;
    Mystruct** mystructures;
} ;

answered Aug 02 '15 at 09:09

this

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score 1 · Answer 2 · answered Aug 02 '15 at 09:11

1

You MUST use "struct Mystruct" only when defining the struct. Once you typedef it to "Mystruct" you can use "Mystruct" anywhere you want.

answered Aug 02 '15 at 09:11

Mateo Hrastnik

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C recursive typedef structures

2 Answers2