git.ozlabs.org Git - ccan/blob - ccan/container_of/_info

   1 #include "config.h"
   2 #include <stdio.h>
   3 #include <string.h>
   4
   5 /**
   6  * container_of - routine for upcasting
   7  *
   8  * It is often convenient to create code where the caller registers a pointer
   9  * to a generic structure and a callback.  The callback might know that the
  10  * pointer points to within a larger structure, and container_of gives a
  11  * convenient and fairly type-safe way of returning to the enclosing structure.
  12  *
  13  * This idiom is an alternative to providing a void * pointer for every
  14  * callback.
  15  *
  16  * Example:
  17  *      #include <stdio.h>
  18  *      #include <ccan/container_of/container_of.h>
  19  *
  20  *      struct timer {
  21  *              void *members;
  22  *      };
  23  *
  24  *      struct info {
  25  *              int my_stuff;
  26  *              struct timer timer;
  27  *      };
  28  *
  29  *      static void my_timer_callback(struct timer *timer)
  30  *      {
  31  *              struct info *info = container_of(timer, struct info, timer);
  32  *              printf("my_stuff is %u\n", info->my_stuff);
  33  *      }
  34  *
  35  *      static void register_timer(struct timer *timer)
  36  *      {
  37  *              (void)timer;
  38  *              (void)my_timer_callback;
  39  *              //...
  40  *      }
  41  *
  42  *      int main(void)
  43  *      {
  44  *              struct info info = { .my_stuff = 1 };
  45  *
  46  *              register_timer(&info.timer);
  47  *              // ...
  48  *              return 0;
  49  *      }
  50  *
  51  * License: CC0 (Public domain)
  52  * Author: Rusty Russell <rusty@rustcorp.com.au>
  53  */
  54 int main(int argc, char *argv[])
  55 {
  56         if (argc != 2)
  57                 return 1;
  58
  59         if (strcmp(argv[1], "depends") == 0) {
  60                 printf("ccan/check_type\n");
  61                 return 0;
  62         }
  63
  64         return 1;
  65 }