Question

I tried to deallocate memory in dict_free() function, but it doesn’t work and I don’t no why. Am I missing something? Can’t figure out, what’s wrong.

Edit:
If I call free() in dict_free() I expect to see that free’d pointer points to NULL, but that’s not happening.

Here is my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct Dict
{
  struct Dict *branches[256];
  int index;

}Dict;


void dict_insert_depth(unsigned char*,Dict *,int);
void dict_insert(unsigned char*,Dict *);

void dict_free(Dict *d)
{
  if(d!=NULL){
    int i;
    for(i=0; i<256; i++){
      if(d->branches[i] != NULL){
        dict_free(d->branches[i]);
        free(d->branches[i]);
        printf("Is it free??  %s\n",d==NULL?"yes":"no");
      }
    }
  }
}
/**
 * Insert word into dictionaR
 */
void dict_insert(unsigned char *w, Dict *d)
{
  dict_insert_depth(w,d,0);
}

void dict_insert_depth(unsigned char *w, Dict *d, int depth)
{
  if(strlen(w) > depth){
    int ch = w[depth];

    if(d->branches[ch]==NULL){
      d->branches[ch] = malloc(sizeof(struct Dict));
      dict_insert_depth(w,d->branches[ch],depth+1);

    }else{
      dict_insert_depth(w,d->branches[ch],depth+1);
    }
  }
}

/**
 * Check whether a word exists in the dictionary
 * @param w Word to be checked
 * @param d Full dictionary
 * @return If found return 1, otherwise 0
 */
int in_dict(unsigned char *w, Dict *d)
{
  return in_dict_depth(w,d,0);
}

int in_dict_depth(unsigned char *w, Dict *d, int depth)
{
  if(strlen(w)>depth){
    int ch = w[depth];
    if(d->branches[ch]){
      return in_dict_depth(w, d->branches[ch], depth+1);
    }else{
      return 0;
    }
  }else{
    return 1;
  }

}

Answer 1

Your free code looks fine, except it will fail to free the root node.

Your test for free-ness is wrong. free will not set any variable to NULL. Often it is a good idea to do that explicitly, so you are sure not to read already freed memory:

    free(d->branches[i]);
    d->branches[i] = NULL;   // clobber pointer to freed memory

To handle the root node issue, and probably somewhat cleaner as well, do this:

void dict_free(Dict *d)
{
  if(d!=NULL){
    int i;
    for(i=0; i<256; i++){
      if(d->branches[i] != NULL){
        dict_free(d->branches[i]);
        d->branches[i] = NULL;
      }
    }
    free(d);
  }
}