Compiler Warning: Initialization incompatible pointer type

Question

I am new to C, and I can't figure it out, why I am getting initialization incompatible poniter type warning.The relevant parts of the code are:

struct a {
  int address;
  B * apples[8];
} A;

struct b {
  int color;
} B;

I have an array of A's called a_list. What I am currently doing is:

B *b_list = a_list[i].apples;   // i being an index in for loop
b_list[6].color = 0;

The above works correctly, but throws the warning:

  Initialization from incompatible pointer type.

In order to fix it, my reasoning is that I should be doing

B ** b_list = a_list[i].apples;  // as it is pointer to pointer. 
So now b_list basically points to a pointer which points to an array of 6, yea?
So: (*b_list)[6].color          // However this causes segmentation fault.

It was also working correctly when the struct A had B apples[8], rather than B* apples[8]. However, using this solution does not maintain the changes made in functions outside of where they were made.

Please advice.

score 1 · Answer 1 · answered Oct 19 '11 at 18:07

1

A and B are not types, but instances of struct a and struct b. Perhaps you want to use the classic C idiom but you are missing a typedef:

typedef struct a {
    ...
} A;

Now struct a and A are the same thing.

In your last code snippet, (*b_list)[6].color should actually be (*b_list[6]).color or better yet b_list[6]->color.

answered Oct 19 '11 at 18:07

K-ballo

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Both the above causes segmentation faults. Is it because some blocks haven't been malloced? – Catie Oct 19 '11 at 18:12
@Catie: Have you allocated each of the `B`s in the array? – K-ballo Oct 19 '11 at 18:13

score 0 · Accepted Answer · answered Oct 19 '11 at 18:06

It was also working correctly when the struct A had B apples[8], rather than B* apples[8]. However, using this solution does not maintain the changes made in functions outside of where they were made.

Pass a pointer to the object to such functions and your changes will persist outside of them. The reason they didn't is because you were passing the object by value.

Compiler Warning: Initialization incompatible pointer type

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