compilation error: request for member in something not a structure or union

Question

Edit: The code below has been modified to work as the problem has been solved.

Specifically, (*hardwareList.next_item)->next was originally written without brackets (e.g. as *hardwareList.next_item->next) and the compiler didn't understand it.

I'm trying to workout why the compiler is getting confused with my C code. I'm trying to create a linked list that stores all the items and also a pointer to the address-of the last "next" variable, for easy appending.

typedef struct {
  int recordNum;
  char toolName[25];
  int quantity;
  float cost;
} HardwareData;

typedef struct _HardwareListItem{
  HardwareData data;
  struct _HardwareListItem* next;
} HardwareListItem;

typedef struct _HardwareList {
  HardwareListItem* items;
  HardwareListItem** next_item;
} HardwareList;

HardwareList readFromFile(FILE* fp)
{
  char stopReading = 0;
  HardwareList hardwareList = {0};
  hardwareList.next_item = &hardwareList.items;
  do {
    *hardwareList.next_item = (HardwareListItem*)calloc(1, sizeof(HardwareData));
    if (*hardwareList.next_item == NULL)
    {
      fprintf(stderr, "OOM Reading File\n");
      fflush(stderr);
      exit(EXIT_FAILURE);
    }
    if (fread(&((*hardwareList.next_item)->data), sizeof(HardwareData), 1, fp) != 1) {
      free(*hardwareList.next_item);
      *hardwareList.next_item = NULL;
      stopReading = 1;
    } else {
      hardwareList.next_item = &((*hardwareList.next_item)->next);
    }
  } while(!stopReading);

  return hardwareList;
}

Compiler says:

line 31: error: request for member 'data' in something not a structure or union
line 36: error: request for member 'next' in something not a structure or union

Mariannamarianne

The compiler doesn't give line numbers? Bad compiler... – Autosuggestion

(hardwareList.next_item)->next won't work as next_item is not a ptr to a struct – Carolanncarole

@QuentinUK: Whoops, my bad. I'll edit in a sec. – Mariannamarianne

@Aaron-Digulla: Compiler did give line numbers but they wouldn't have matched up with what I copied in.. Edited now with new line numbers. – Mariannamarianne

In that case add a comment to the pasted code like which contains the error message :-) – Autosuggestion

https://mcmap.net/q/223022/-what-does-quot-request-for-member-39-39-in-something-not-a-structure-or-union-quot-mean/1111160 – Disinter

Answer 1

My guess the problem is this piece of code: *(hardwareList.next_item)->data

next_item is a pointer to a pointer, so my guess is that the compiler reads this as *((hardwareList.next_item)->data) which of course doesn't work - pointers don't have any members in C.

Try ((*(hardwareList.next_item))->data) to get the correct dereference order.

Autosuggestion

Thanks heaps, this has been driving me insane thinking about how I've got it wrong. – Mariannamarianne

Answer 2

hardwareList.next_item is HardwareListItem**, so operator -> on it returns HardwareListItem*, which obviously is not a struct.

You're using too many pointers, it is confusing. Try to simplify your code, you have tons of bugs there.

Arezzo

I've tried to simplify (see updated code above), but still pretty confusing. – Mariannamarianne