Question

I know that there’s something fishy about the malloc part, but I’m having trouble seeing what’s unsafe about this:

//que structure
typedef struct queue{
         int *que;  // the actual array of queue elements
         int head;   // the head index in que of the queue
         int count;  /// number of elements in queue
         int size; // max number of elements in queue
    } QUEUE;


void qManage(QUEUE **qptr, int flag, int size){
      if(flag){
              /* allocate a new queue */
              *qptr = malloc(sizeof(QUEUE));
              (*qptr)->head = (*qptr)->count = 0;
              (*qptr)->que = malloc(size * sizeof(int));
              (*qptr)->size = size;
    }
    else{
             /* delete the current queue */
             (void) free((*qptr)->que);
             (void) free(*qptr);
    }
}

Answer 1

I’m pretty sure the problem this:
What happens if you pass a negative value for 'size'?

Another possible issue is that you do not check *qptr for NULL after you allocate, however, rarely would that be a problem in actual code, if it would ever happen, you have other errors to worry about.