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  1. // Join items on output stream. (3.03)
  2.  
  3. #include <stdio.h>
  4.  
  5. void ostream_join(
  6.     const void *base, size_t nitems, size_t itemsize,
  7.     void (*putitem)(const void *item, FILE *stream),
  8.     const char *separator, FILE *stream, _Bool reverse)
  9. {
  10.     const char *first = base;
  11.     const char *last = first + nitems*itemsize;
  12.  
  13.     if (first != last)
  14.     {
  15.         for (;;) {
  16.             if (reverse)
  17.             {
  18.                 last -= itemsize;
  19.                 putitem(last, stream);
  20.             }
  21.             else
  22.             {
  23.                 putitem(first, stream);
  24.                 first += itemsize;
  25.             }
  26.             if (first == last)
  27.                 break;
  28.             fputs(separator, stream);
  29.         }
  30.     }
  31. }
  32.  
  33. // Specialize.
  34.  
  35. #define DEFINE_PRINTER(name, proc, type)                        \
  36. void name(const type *a, size_t n, int end, _Bool reverse)      \
  37. {                                                               \
  38.     putchar('[');                                               \
  39.     ostream_join(a, n, sizeof *a, proc, ", ", stdout, reverse); \
  40.     putchar(']');                                               \
  41.     if (end != 0)                                               \
  42.         putchar(end);                                           \
  43. }
  44.  
  45. struct point {
  46.     int x, y;
  47. };
  48.  
  49. static void putpoint_(const void *item, FILE *stream)
  50. {
  51.     const struct point *p = item;
  52.     fprintf(stream, "(%d, %d)", p->x, p->y);
  53. }
  54.  
  55. DEFINE_PRINTER(print_points, putpoint_, struct point)
  56.  
  57. int main(void)
  58. {
  59.     struct point a[] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}};
  60.     print_points(a, sizeof a / sizeof *a, '\n', 0);
  61.     print_points(a, sizeof a / sizeof *a, '\n', 1);
  62.     return 0;
  63. }
Success #stdin #stdout 0s 5272KB
comments (?)
stdin
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Standard input is empty
stdout
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[(1, 2), (3, 4), (5, 6), (7, 8)]
[(7, 8), (5, 6), (3, 4), (1, 2)]
https://ideone.com/PPtNsQ
language:
C (gcc 8.3)
created:
10 days ago
visibility:
public

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