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  1. #include <stdlib.h>
  2. #include <stdio.h>
  3. #include <string.h>
  4.  
  5. /*** Object types */
  6.  
  7. typedef struct s_obj s_obj;
  8. typedef struct s_string s_string;
  9. typedef struct s_integer s_integer;
  10.  
  11. /*** Function types */
  12.  
  13. typedef void f_any();
  14. typedef f_any * f_interface(s_obj *, f_any *);
  15.  
  16. typedef char * f_tostring(s_obj *);
  17.  
  18. /*** Function declarations */
  19.  
  20. f_tostring tostring;
  21.  
  22. void init_string(s_string *);
  23. f_interface string_interface;
  24. f_tostring string_tostring;
  25.  
  26. void init_integer(s_integer *);
  27. f_tostring integer_tostring;
  28. f_interface integer_interface;
  29.  
  30. /*** Struct/union definitions */
  31.  
  32. struct s_obj {
  33.     f_interface * get_interface;
  34.   };
  35.  
  36. struct s_string {
  37.     s_obj obj[1];
  38.     char * text;
  39.   };
  40.  
  41. struct s_integer {
  42.     s_obj obj[1];
  43.     int i;
  44.   };
  45.  
  46. /*** Function definitions */
  47.  
  48. int main(void) {
  49.     char * tmp;
  50.     s_string my_string;
  51.     s_integer my_integer;
  52.  
  53.     init_string(&my_string);
  54.     my_string.text = "My string!";
  55.     tmp = tostring(my_string.obj);
  56.     puts(tmp);
  57.     free(tmp);
  58.  
  59.     init_integer(&my_integer);
  60.     my_integer.i = 42;
  61.     tmp = tostring(my_integer.obj);
  62.     puts(tmp);
  63.     free(tmp);
  64.  
  65.     return EXIT_SUCCESS;
  66.   }
  67.  
  68. /* You must 'free' the storage allocated by 'tostring'! */
  69. char * tostring(s_obj * obj) {
  70.     f_tostring * func;
  71.  
  72.     func = (f_tostring *) obj->get_interface(obj, (f_any *) tostring);
  73.     return func(obj);
  74.   }
  75.  
  76. void init_string(s_string * string) {
  77.     string->obj->get_interface = string_interface;
  78.     string->text = NULL;
  79.     return;
  80.   }
  81.  
  82. f_any * string_interface(s_obj * obj, f_any * func) {
  83.     /* Unused */
  84.     (void) obj;
  85.  
  86.     if (0);
  87.     /* 'tostring' case */
  88.     else if (func == (f_any *) tostring)
  89.       return (f_any *) string_tostring;
  90.     /* ...Other cases... */
  91.     /* Unsupported interface */
  92.     exit(EXIT_FAILURE);
  93.   }
  94.  
  95. char * string_tostring(s_obj * obj) {
  96.     s_string * this = (void *) obj;
  97.     char * new;
  98.     int len;
  99.  
  100.     len = strlen(this->text) + 1;
  101.     new = malloc(len);
  102.     if (!new)
  103.       return new;
  104.  
  105.     memcpy(new, this->text, len);
  106.     return new;
  107.   }
  108.  
  109. void init_integer(s_integer * integer) {
  110.     integer->obj->get_interface = integer_interface;
  111.     integer->i = 0;
  112.     return;
  113.   }
  114.  
  115. f_any * integer_interface(s_obj * obj, f_any * func) {
  116.     /* Unused */
  117.     (void) obj;
  118.  
  119.     if (0);
  120.     /* 'tostring' case */
  121.     else if (func == (f_any *) tostring)
  122.       return (f_any *) integer_tostring;
  123.     /* ...Other cases... */
  124.     /* Unsupported interface */
  125.     exit(EXIT_FAILURE);
  126.   }
  127.  
  128. char * integer_tostring(s_obj * obj) {
  129.     s_integer * this = (void *) obj;
  130.     char tmp[50];
  131.     char * new;
  132.     int len;
  133.  
  134.     sprintf(tmp, "%d", this->i);
  135.     len = strlen(tmp) + 1;
  136.     new = malloc(len);
  137.     if (!new)
  138.       return new;
  139.  
  140.     memcpy(new, tmp, len);
  141.     return new;
  142.   }
  143.  
Success #stdin #stdout 0.02s 1852KB
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Standard input is empty
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My string!
42
https://ideone.com/m1z5p
language:
C (gcc 8.3)
created:
12 years ago
visibility:
public

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