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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3.  
  4. typedef struct snake snake;
  5. struct snake {
  6.     int x; /* x coordinate */
  7.     int y; /* y coordinate */
  8.     snake *previous;
  9.     snake *next;
  10. };
  11.  
  12. snake *initSnake(void) {
  13.     snake *pointer, *tmp1, *tmp2 = NULL;
  14.     /* three iterations, so the snake will have a length of three */
  15.     for( int i = 0; i<3; i++) {
  16.         if(NULL == (tmp1 = (snake*)malloc(sizeof(snake)))) {
  17.             return NULL;
  18.         }
  19.         /* coordinates */
  20.         tmp1->x = 20;
  21.         tmp1->y = 10 + i;
  22.         /* first previous points to NULL */
  23.         tmp1->previous = tmp2;
  24.         if (tmp2)
  25.            tmp2 -> next = tmp1; 
  26.         /* temporarily store last pointer to be used for next previous pointer */
  27.         tmp2 = tmp1;
  28.         if(0 == i) {
  29.             /* store first pointer so it can be returned */
  30.             pointer = tmp1;
  31.         }
  32.  
  33.     }
  34.     /* the last next pointer has to point to NULL */
  35.     tmp1->next = NULL;
  36.     /* now return the pointer to the first element in list */
  37.     return pointer;
  38. }
  39.  
  40.  
  41. int main() {
  42.     /* pointer to first element in list */
  43.     snake *head = NULL;
  44.  
  45.     if(NULL == (head = initSnake() ) ) {
  46.         fprintf(stderr, "Not enough memory!\n");
  47.         return EXIT_FAILURE;
  48.     }
  49.     /* here everything works fine */
  50.     printf("%d\n", head->y);
  51.     printf("%d\n", head->previous);
  52.     /* when trying to acces the content of the next element, the program crashes... */
  53.     printf("%d\n", head->next->x);
  54.     /* pause */
  55.     getchar();
  56. }
  57.  
Success #stdin #stdout 0s 3460KB
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Standard input is empty
stdout 
10
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https://ideone.com/ifNqJa
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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