C - void*

void* pop_from_queue(queue_t *queue)

typedef struct {
   int end;
   int size;
   void *list;
} queue_t;

bool push_to_queue(queue_t *queue, void *data){
        ...
   queue->list[queue->end] = data;
   ...
};

return (void*)output;

In file included from queue.c:1:
./queue.h:20:29: warning: invalid application of 'sizeof' to a void type
      [-Wpointer-arith]
        sm->list = malloc(sm->size*sizeof(void));
                                   ^     ~~~~~~
./queue.h:18:2: warning: variable 'sm' is uninitialized when used here
      [-Wuninitialized]
        sm->end = 0;
        ^~
./queue.h:17:13: note: initialize the variable 'sm' to silence this warning
        queue_t *sm;
                   ^
                    = NULL
./queue.h:38:13: warning: subscript of a pointer to void is a GNU extension
      [-Wpointer-arith]
        queue->list[queue->end] = data;
        ~~~~~~~~~~~^
./queue.h:38:26: error: incomplete type 'void' is not assignable
        queue->list[queue->end] = data;
        ~~~~~~~~~~~~~~~~~~~~~~~ ^
./queue.h:53:20: warning: subscript of a pointer to void is a GNU extension
      [-Wpointer-arith]
        help = queue->list[0];
               ~~~~~~~~~~~^
./queue.h:53:7: error: assigning to 'void *' from incompatible type 'void'
        help = queue->list[0];
             ^ ~~~~~~~~~~~~~~
./queue.h:57:15: warning: subscript of a pointer to void is a GNU extension
      [-Wpointer-arith]
                        queue->list[i] = queue->list[i+1];
                        ~~~~~~~~~~~^
./queue.h:57:32: warning: subscript of a pointer to void is a GNU extension
      [-Wpointer-arith]
                        queue->list[i] = queue->list[i+1];
                                         ~~~~~~~~~~~^
./queue.h:57:19: error: incomplete type 'void' is not assignable
                        queue->list[i] = queue->list[i+1];
                        ~~~~~~~~~~~~~~ ^
./queue.h:74:21: warning: subscript of a pointer to void is a GNU extension
      [-Wpointer-arith]
                return queue->list[idx];
                       ~~~~~~~~~~~^
./queue.h:74:10: error: returning 'void' from a function with incompatible
      result type 'void *'
                return queue->list[idx];
                       ^~~~~~~~~~~~~~~~