#include <stdio.h>
#include <stdlib.h>

#define local_type  __attribute__ ((cleanup(my_free)))

static void my_free(void* pmem)//the type of paramter must be a void pointer
{
      printf("pmem=%p...\n", pmem);
      printf("&pmem=%p...\n", &pmem);
      void** ppmem = (void**) pmem;
      printf("*ppmem=%p...\n", *ppmem);
      free(*ppmem);
}

#if 0
//warning: passing argument 1 of ‘my_free’ from incompatible pointer type
static void my_free(void** ppmem)
{
      printf("ppmem=%p...\n", ppmem);
      printf("*ppmem=%p...\n", *ppmem);
}
#endif

int foo(void)
{
    local_type int* p = (int*) malloc(sizeof(int));
    printf("do something, p=%p\n", p);

    return 0;
}

int main(int argc, char** argv)
{

    foo();
    // when return, the memory block pointed by p is freed automatically
    printf("11111111\n");

    return 0;
}

 1 #include <stdlib.h>
 2 #include <stdio.h>
 3 
 4 struct shared_ptr_s
 5 {
 6     //    struct impl_t* inst;
 7     int *use_cnt;
 8 };
 9 
10 typedef struct shared_ptr_s shared_ptr_t;           // unadorned type
11 #define shared_ptr struct shared_ptr_s __attribute__((cleanup(free_shared)))
12 
13 #define SHARED_PTR_GET_ADD_REF(sp_in, sp_name) ++(*sp_in.use_cnt); 14                         printf("add use_cnt = %d, sp_in=%p\n", *sp_in.use_cnt, sp_in); 15                         shared_ptr sp_name = sp_in; 16                         printf("&sp_name=%p, sp_name:%p\n", &sp_name, sp_name);
17 
18 void free_shared(struct shared_ptr_s* ptr)
19 {
20     printf("ptr:%p, usr_cnt:%p\n", ptr, ptr->use_cnt);
21     if(!ptr) return;
22     printf("del use_cnt = %d\n", *ptr->use_cnt - 1); 
23     if(0 == --(*ptr->use_cnt)) {
24         //dtor(ptr->inst);
25         printf("freeing %p\n", (void *)ptr->use_cnt);
26         free(ptr->use_cnt);
27     }
28     //ptr->inst = 0;
29     ptr->use_cnt = 0;
30 }
31 
32 void func(shared_ptr_t sp)
33 {
34     SHARED_PTR_GET_ADD_REF(sp, sp_loc);
35     printf("111111111\n");
36     return;
37 }
38 
39 int main(void)
40 {
41     shared_ptr_t sp = {         // original type does not use __attribute__(cleanup)
42         //.inst = ctor(), 
43         .use_cnt = malloc(sizeof(int)) 
44     };
45     printf("use_cnt content addr:%p, &use_cnt=%p, &sp=%p,sp=%p\n", sp.use_cnt, &sp.use_cnt, &sp,sp);
46     SHARED_PTR_GET_ADD_REF(sp, sp_loc);
47 
48     printf("222222222222\n");
49     func(sp_loc);
50     printf("333333333\n");
51 
52     return 0;
53 }