c - Freeing an array within a struct -

for assignment have write circular queue (which imagine of familiar with). made structure , function initializes queue struct using dynamic memory. note have array arr within struct assign memory.

for reason can't seem free array memory.

struct queue {   element_t *arr;    // dynamic array containing data elements   int current_size;   // counts number of elements in queue   int front, rear;   // remark later: fields need added here make thread-safe queue needed assigment };   queue_t* queue_create(){   struct queue *queue = malloc(sizeof(struct queue));    if(queue == 0){  //check if memory available     printf("out of memory\n");     return null;   }    queue -> current_size = 0;   queue -> front = -1;   queue -> rear = -1;   queue -> arr = malloc(queue_size*sizeof(element_t));   return queue; } 

i'm trying free memory when i'm done using function queue_free. function takes in double pointer queue (part of assignment).

void queue_free(queue_t** queue){   free(**queue -> arr);   free(*queue); } 

when call last function got error message saying:

queue.c: in function ‘queue_free’: queue.c:39:16: error: request member ‘arr’ in not structure or union    free(**queue -> arr);                 ^ 

i've checked valgrind leaks. queue gets freed correctly reason can't address of array.

thanks in advance

p.s. free(queue -> arr); free(*queue -> arr); , free(**queue -> arr); fail , generate same error message.

the free statement should free((*queue)->arr).

explanation: queue_free defines queue variable pointer pointer queue_t struct. now, in order pointer struct need remove 1 level of indirection using (*queue); can use dereference operator -> access arr member.

now, reason why other options didn't work are:

• free(queue -> arr) - pointer pointer of queue_t structure not have arr member
• free(*queue -> arr) - dereference operator ('*') refers whole expression, i.e. queue->arr, takes previous error
• free(**queue -> arr) - same above