Thread: Unexplained Crashing

Hello all,

I'm currently looking at a very simple program which will read some information from a file, store this in a binary tree, then print it to the screen.
Unfortunately, I'm having problems with it. The program is doing one of those annoying things where it isn't giving me any errors or warning, just crashing when I execute it.

Heres the code for you to digest :

Code:

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

/* construct tree */

struct node
{
   char *word;
   struct node *left,*right;
};

/* insert into tree*/

struct node *inserttree(struct node *tree, char *s)
{
   int i;
   
   if ( tree==NULL )
   {
      if ( (tree=(struct node *) malloc(sizeof (struct node)))!=NULL )
         if ( (tree->word=(char *) malloc(strlen(s)+1))==NULL )
         {
            free(tree);
            tree = NULL;
         }
         else
         {
            tree->left = NULL;
            tree->right = NULL;
            strcpy(tree->word, s);
         }
   }
   else if ( i = strcmp(tree->word, s) > 0 )
      tree->left = inserttree(tree->left, s);

   else if ( i < 0 )
      tree->right = inserttree(tree->right, s);

   else
      return tree;
}

/* print to console*/

void printtree(struct node *tree, FILE *outf)
{
     
   if ( tree != NULL )
   {
      printtree(tree->left, outf);
      printf("&#37;s\n", tree->word);
      printtree(tree->right, outf);
   }
}

/* destroy tree */

void freetree(struct node *tree)
{
   if ( tree!=NULL )
   {
      free(tree->word);
      freetree(tree->left);
      freetree(tree->right);
      free(tree);
   }
}


int main(void)
{

   FILE *f,*outf;

   char s[100]; 

   struct node *tree=NULL;
   

   if ( (f=fopen("test.txt","r")) == NULL )
   {
      printf("Unable to open test.txt\n");
      system("PAUSE");
   }

   else
   {
      while ( fscanf(f,"%99s",s)!= EOF )
      {
         tree=inserttree(tree, s);
         printtree(tree, f);
      }
      fclose(f);
   }

   return 0;
}

Does anything jump out at anyone as a problem?
Thanks for the help.

Adding assumed headers, beautifying, and attempting to build:

Code:

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

/* construct tree */

struct node
{
   char *word;
   struct node *left,*right;
};

/* insert into tree*/

struct node *inserttree(struct node *tree, char *s)
{
   int i;

   if ( tree==NULL )
   {
      if ( (tree=(struct node *) malloc(sizeof (struct node)))!=NULL )
         if ( (tree->word=(char *) malloc(strlen(s)+1))==NULL )
         {
            free(tree);
            tree = NULL;
         }
         else
         {
            tree->left = NULL;
            tree->right = NULL;
            strcpy(tree->word, s);
         }
   }
   else if ( (i = strcmp(tree->word,s))>0 )
      tree->left = inserttree(tree->left, s);

   else if ( i< 0 )
      tree->right = inserttree(tree->right, s);

   else
      return tree;
}

/* print to console*/

void printtree(struct node *tree, FILE *outf)
{
   if ( tree!=NULL )
   {
      printtree(tree->left,outf);
      printf("%s\n", outf/*tree->word*/);
      printtree(tree->right, outf);
   }
}

/* destroy tree */

void freetree(struct node *tree)
{
   if ( tree!=NULL )
   {
      free(tree->word);
      freetree(tree->left);
      freetree(tree->right);
      free(tree);
   }
}


int main(void)
{

   FILE *f,*outf;

   char s[100]; 

   struct node *tree=NULL;

   if ( (f=fopen("words.txt","r")) == NULL )
   {
      printf("Unable to open word.txt\n");
      system("PAUSE");
   }

   else
   {
      while ( fscanf(f,"%100s",s)!= EOF )
      {
         tree=inserttree(tree, s);
         fclose(f);
         printtree(tree, outf);
         freetree(tree);
      }
      fclose(outf);
   }

   return 0;
}

main.c
main.c: In function `inserttree':
main.c:21: warning: suggest explicit braces to avoid ambiguous `else'
main.c:42: warning: control reaches end of non-void function
main.c: In function `printtree':
main.c:51: warning: char format, FILE arg (arg 2)
Linking...
Build successful

Did you fix this yet?

Code:

printf("%s\n", outf/*tree->word*/);

Why do you free the whole tree and close the file after every record?
Do you know your fscanf format specifier is off by one too many?
Have you tried stepping through the debugger?
Would you care to make the input file available?
Why C++ since this is C?

Originally Posted by Swordsman

The input file is nothing but gibberish, just a few words in a text file, nothing special, although it if makes a difference I can post it.

I would like to see what you see. Especially now that the code is very different from the last time you posted it.

I'm just taking a stab in the dark here but this does look rather suspicious to me.

It could be that on some execution paths of your inserttree function that i contains an undefined value that will almost certainly be greater than zero, or just... not what you're expecting i to be. This would cause code that normally would not be executed to execute anyway.

> else if((i = strcmp( tree->word, s ) > 0)
I tried to make some other point about how ugly this was, but I was wrong about that. Pretty much, this is the only path where i has a defined value.

So have you run it in the debugger, and single stepped your way through it?

What about removing the file stuff, and testing with a main of

Code:

   struct node *tree=NULL;
   tree=inserttree(tree, "does");
   tree=inserttree(tree, "this");
   tree=inserttree(tree, "work");
   printtree(tree, stdout);

If that crashes, then you have a nice simple test case.
If not, then you can expand into reading from files.


> printtree(tree, f);
Why are you (trying) printing to the file you're reading from?