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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <string.h>
  4. #include <assert.h>
  5.  
  6. typedef struct { 
  7.     int x, y; 
  8. } Point;
  9.  
  10. typedef struct {
  11.     char label[8];
  12.     const char *desc;
  13.     Point vertices[];  // Flexible array member
  14. } Polygon;
  15.  
  16. Polygon *make_polygon(const char *label, const char *desc, size_t nPoints, Point vertices[nPoints]) {
  17.     // Allocate memory for the Polygon structure and its vertices array
  18.     Polygon *p = malloc(sizeof(Polygon) + nPoints * sizeof(Point));
  19.  
  20.     // Ensure the label can fit into the structure
  21.     assert(strlen(label) < sizeof(p->label));
  22.  
  23.     // Copy label and description to the polygon
  24.     strcpy(p->label, label);
  25.     p->desc = desc;
  26.  
  27.     // Copy the vertices array into the polygon
  28.     memcpy(p->vertices, vertices, nPoints * sizeof(Point));
  29.  
  30.     return p;
  31. }
  32.  
  33. void f() {
  34.     // Create a triangle polygon using `make_polygon()`
  35.     Polygon *triangle = make_polygon("tr_1", "base", 3, (Point[]) {
  36.         { .x = 0, .y = 0 },
  37.         { .x = 64, .y = 10 },
  38.         { .x = 100, .y = 32 }
  39.     });
  40.  
  41.     // Access the 3rd vertex
  42.     Point *v2 = &triangle->vertices[2];
  43.  
  44.     // Get the x-coordinate of the 3rd vertex
  45.     int x2 = v2->x;
  46.  
  47.     // Access a byte after the x value of the 3rd vertex
  48.     char c = *((char *)(&v2->x) + 4);  // This accesses the memory directly
  49.  
  50.     // Clean up allocated memory
  51.     free(triangle);
  52. }
  53.  
  54. int main() {
  55.     printf("Start\n");
  56.     f();
  57.     printf("End");
  58.     return 0;
  59. }
Success #stdin #stdout 0s 5284KB
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Start
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https://ideone.com/t9EtRB
language:
C (gcc 8.3)
created:
6 days ago
visibility:
public

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