List with a head as double pointer

Question

If i have a list of lists as

typedef Struct b {
int b;
Struct b *next;
}B;

typedef Struct a {
int a;
Struct a *next;
B *link;
}A;

and if i develop the data structure following this scheme.. enter image description here

I use a double pointer as head for B for keep track of all the nodes of B between the A nodes. So if i use realloc to give more data to the pointer, i will not lose previously allocated data inside the head, right ?

for(i=0;i<n_of_B_lists;i++)
  *head_b[i]=realloc(*head_b[i],sizeof(B *)*1); //1 is for 1 pointer to the new B list

[Be careful with your operator precedence](http://en.cppreference.com/w/c/language/operator_precedence) — WhozCraig, Jan 04 '15 at 21:07
@WhozCraig I'ts wiered that I used the same words that you used, without seeing your comment, and when you commented it was not in my answer, when I was writing the example of a better usage of `realloc`, I noticed that the OP may not know the difference between `(*head_b)[i]` and `*(head_b[i])`. — Iharob Al Asimi, Jan 04 '15 at 21:11

score 1 · Answer 1 · answered Jan 04 '15 at 21:06

Yes that's what realloc is exactly for, though I would recommend a different way of using it, just

void *temp;

temp = realloc(*head_b[i], sizeof(B *));
if (temp == NULL)
    doSomethingReallocFailed();
*head_b[i] = temp;

also be careful with operator precedence in the *head_b[i] expression.

List with a head as double pointer

1 Answers1