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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <string.h>
  4.  
  5.  
  6. struct nlist {
  7.         struct nlist *next;
  8.         char *name;
  9.         char *defn;
  10. };
  11.  
  12. #define HASHSIZE 101
  13. static struct nlist *hashtab[HASHSIZE];
  14.  
  15. unsigned hash (char *s)
  16. {
  17.         unsigned hashval;
  18.  
  19.         for (hashval = 0; *s != '\0'; s++)
  20.                 hashval += *s + 31 * hashval;
  21.         return hashval % HASHSIZE;
  22. }
  23.  
  24. struct nlist * lookup (char *s)
  25. {
  26.         struct nlist *np;
  27.  
  28.         for (np = hashtab[hash(s)]; np != NULL; np = np->next)
  29.                 if (strcmp(s, np->name) == 0)
  30.                         return np;
  31.         return NULL;
  32. }
  33.  
  34. struct nlist * install (char *name, char *defn)
  35. {
  36.         struct nlist *np;
  37.         unsigned hashval;
  38.  
  39.         if ((np = lookup(name)) == NULL)
  40.         {
  41.                 np = (struct nlist *) malloc(sizeof(*np));
  42.                 if (np == NULL || (np->name = strdup(name)) == NULL)
  43.                         return NULL;
  44.                 hashval = hash(name);
  45.                 np->next = hashtab[hashval];
  46.                 hashtab[hashval] = np;
  47.         }
  48.         else
  49.                 free ((void *) np->defn);
  50.                 if ((np->defn = strdup(defn)) == NULL)
  51.                         return NULL;
  52.                 return np;
  53. }
  54.  
  55. void undef (char *name)
  56. {
  57.         struct nlist *curr, *last;
  58.         unsigned hashval;
  59.  
  60.         last = curr = hashtab[hash(name)];
  61.         while (curr != NULL && strcmp(name, curr->name)!= 0)
  62.         {
  63.                 printf("while loop\n");
  64.                 last = curr;
  65.                 curr = curr->next;
  66.                 printf("last = %x, curr = %x\n", last, curr);
  67.         }
  68.  
  69.         printf("after loop\n");
  70.         if (curr)
  71.         {
  72.                 last->next = curr->next;
  73.                 // !!!!!!!!
  74.                 free (curr);
  75. 				free ((void *) curr->name);
  76. 				free ((void *) curr->defn);
  77.         }
  78. }
  79.  
  80.  
  81. int main (int argc, char *argv[])
  82. {
  83.         printf ("%u\n", hash("abcdef"));
  84.         install ("H", "127");
  85.         printf ("%s\n", lookup("H")->defn);
  86.  
  87.         undef ("H");
  88.       if (lookup("H") != NULL)
  89.               printf ("%s\n", lookup("H")->defn);
  90. }
Success #stdin #stdout 0s 2244KB
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after loop
https://ideone.com/CZ7nTT
language:
C (gcc 8.3)
created:
8 years ago
visibility:
public

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