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  1.     #include <stdio.h>
  2.     #include <stdlib.h>
  3.     #include <errno.h>
  4.  
  5.     typedef int abstract_func_type ();
  6.  
  7.     typedef struct htentry {
  8.         struct htentry *next;
  9.         abstract_func_type *k;
  10.         abstract_func_type **fpp;
  11.     } htentry;
  12.     static htentry *hashtable[101];
  13.  
  14.     static void insert (abstract_func_type *k, abstract_func_type **p) {
  15.         htentry *e = malloc(sizeof(htentry));
  16.         int i = ((char *)k - (char *)0) % 101;
  17.         e->k = k;
  18.         e->fpp = p;
  19.         e->next = hashtable[i];
  20.         hashtable[i] = e;
  21.     }
  22.  
  23.     static abstract_func_type ** lookup (abstract_func_type *k) {
  24.         int i = ((char *)k - (char *)0) % 101;
  25.         htentry *e = hashtable[i];
  26.         while (e) {
  27.             if (e->k == k) return e->fpp;
  28.             e = e->next;
  29.         }
  30.         return 0;
  31.     }
  32.  
  33.     abstract_func_type * abstract_func_get (abstract_func_type *k) {
  34.         abstract_func_type **f = lookup(k);
  35.         if (f) return *f;
  36.         return 0;
  37.     }
  38.  
  39.     int abstract_func_set (abstract_func_type *k, abstract_func_type *p) {
  40.         abstract_func_type **f = lookup(k);
  41.         if (f) {
  42.             *f = p;
  43.             return 0;
  44.         }
  45.         return -ENOENT;
  46.     }
  47.  
  48.     #define DEFINE_ABSTRACT_FUNC(func) \
  49.         static int static_##func (); \
  50.         static abstract_func_type *func##_ptr = static_##func; \
  51.         int func () { return func##_ptr(); } \
  52.         static int static_##func ()
  53.  
  54.     DEFINE_ABSTRACT_FUNC(foo) { return puts("foo"); }
  55.     DEFINE_ABSTRACT_FUNC(bar) { return puts("bar"); }
  56.  
  57.     void abstract_func_init () {
  58.         insert(foo, &foo_ptr);
  59.         insert(bar, &bar_ptr);
  60.     }
  61.  
  62.     void swap(abstract_func_type *a, abstract_func_type *b) {
  63.         abstract_func_type *ap = abstract_func_get(a);
  64.         abstract_func_type *bp = abstract_func_get(b);
  65.         abstract_func_set(a, bp);
  66.         abstract_func_set(b, ap);
  67.     }
  68.  
  69.     int
  70.     main ()
  71.     {
  72.         abstract_func_init();
  73.         puts("before swap");
  74.         foo();
  75.         bar();
  76.         swap(foo, bar);
  77.         puts("after swap");
  78.         foo();
  79.         bar();
  80.         return 0;
  81.     }
  82.  
Success #stdin #stdout 0s 1964KB
comments (?)
stdin
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Standard input is empty
stdout
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before swap
foo
bar
after swap
bar
foo
https://ideone.com/WxG8CQ
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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