How to free double pointer in Queue [C language]?

Question

When calling deleteQueue:

Exception thrown at 0x00007FF8E378169C (ucrtbased.dll) in LoadBalancer.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Create queue function:

queue_t* createQueue(unsigned capacity){
    queue_t* queue = (queue_t*)malloc(sizeof(queue_t));

    if (queue == NULL)
    {
        return NULL;
    }

    queue->capacity = capacity;
    queue->array = (char**)malloc(sizeof(char*) * queue->capacity);
    queue->size = 0;
    queue->front = 0;
    queue->rear = -1;

    InitializeCriticalSection(&(queue->cs));

    return queue;
}

Enqueue:

void enqueue(queue_t* queue, char* string){

    EnterCriticalSection(&(queue->cs));

    if (isFull(queue)) {
        LeaveCriticalSection(&(queue->cs));
        return;
    }

    queue->rear = (queue->rear + 1) % queue->capacity;
    queue->size = queue->size + 1;

    char* ptr = (char*)malloc(strlen(string)+1);
    memcpy(ptr, string, strlen(string)+1);

    queue->array[queue->rear] = ptr;

    LeaveCriticalSection(&(queue->cs));

    return;
}

Delete queue function:

void deleteQueue(queue_t* queue){
    DeleteCriticalSection(&(queue->cs));
    if (queue != NULL)
    {
        for (int i = 0; i < queue->capacity; i++) {
            free(queue->array[i]);
        }

        free(queue->array);
        free(queue);
    }
}

And should I free the pointer as well in dequeue program breaks with the same exception?

char* dequeue(queue_t* queue){
    EnterCriticalSection(&(queue->cs));
    
    if (isEmpty(queue)) {
        LeaveCriticalSection(&(queue->cs));
        return NULL;
    }

    char* temp = queue->array[queue->front];


    queue->front = (queue->front + 1) % queue->capacity;
    queue->size = queue->size - 1;



    LeaveCriticalSection(&(queue->cs));

    return temp;
}

Answer 1

For starters you allocated an array of pointers that has indeterminate values.

queue->array = (char**)malloc(sizeof(char*) * queue->capacity);

So using this loop within the function deleteQueue

for (int i = 0; i < queue->capacity; i++) {
    free(queue->array[i]);
}

can invoke undefined behavior. You should initialize the array with a null pointer. For example instead of using the function malloc you could use the function calloc.

Secondly within the function dequeue after this statement

char* temp = queue->array[queue->front];

you should write

queue->array[queue->front] = NULL;

It is the responsibility of the user to free the returned string.