Thread: strcmp segfault ?

Im having trouble finding what my problem is..

Im writing a binary tree library and when I run this test program: (cannot be changed)

Code:

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

void print_name(char *key, void *value){
   printf("&#37;s\n", key);
}

main(int argc, char *argv[]) {
  if (argc <= 1) {
    fprintf(stderr, "usage: bst_test name1 name2 ... namek\n");
    exit(1);
  }
  void *tree = create_tree();
  int i;

  // test inserts
  for (i = 1; i < argc; i++) {
     tree_insert(strdup(argv[i]), (void *)1, tree);
  }

  // test print tree
  print_tree(tree, print_name);

  // test finds
  for (i = 0; i < argc; i++) {
    if (tree_find(argv[i], tree) == 0)
      printf("%s not in data set\n", argv[i]);
  }
}

I get these errors:

Code:

(gdb) bt
#0  0xb7edfd2a in strcmp () from /lib/tls/i686/cmov/libc.so.6
#1  0x0804853e in tree_insert (key=0x804a030 "name", value=0x1,
    tree=0x804a008) at bintree.c:33
#2  0x0804878d in main (argc=3, argv=0xbfe13134) at test.c:22

Here is the library im writing:

Code:

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


typedef struct _node{
    struct _node *children;
    struct _node *next;
    char *name;
    int space;
    int x; //x coordinate
    int y; //y coordinate
} NODE;

typedef struct _bnode{
    char *name;
    struct _node family_node;
    struct _bnode *left;
    struct _bnode *right;
} BNODE;

BNODE *tree_insert(char *key, void *value, void *tree){
    BNODE *root = (BNODE *)tree;
    if(root == 0){
        root = (BNODE *)malloc(sizeof(BNODE));
        if(root != NULL)
        {
            root->name = strdup(key);
            root->left = NULL;
            root->right = NULL;
        }
    }else{
        if(strcmp(key, root->name) < 0){   <--- line 33
            root->left = tree_insert(key, value, root->left);
        }else if(strcmp(key, root->name) > 0){
            root->right = tree_insert(key, value, root->right);
        }else if(strcmp(key, root->name) == 0){
	    root->name = strdup(key);
        }
    }

    return root;
}


BNODE *tree_find(char *key, void *tree){
    BNODE *root = (BNODE *)tree;
    if(root == 0){
        return 0;
    }
    if(strcmp(key, root->name) < 0){
        return tree_find(key, root->left);
    }else if(strcmp(key, root->name) > 0){
        return tree_find(key, root->right);
    }else{
        return root;
    }
}


void *create_tree(){
    BNODE *new_tree = (BNODE *)malloc(sizeof(BNODE));
    new_tree->left = NULL;
    new_tree->right = NULL;

}

void print_tree(void *tree, void(*print_fct)(char *key, void *value)){
    BNODE *current = (BNODE *)tree;

    if(current == NULL || print_fct == NULL){
        return;
    }else{
        print_tree(current->left, print_fct);

        print_fct(current->name, (void *)current->family_node.space);

        print_tree(current->right, print_fct);
    }

}

In the else case, you KNOW root is NULL; that's the only way you can get there. And yet you try to follow root->name anyway? Why? Looking at it, the != case should be the == case, and vice versa.

Originally Posted by matsp

Code:

  void *tree = create_tree();
...
void *create_tree(){
    BNODE *new_tree = (BNODE *)malloc(sizeof(BNODE));
    new_tree->left = NULL;
    new_tree->right = NULL;

}

What is the return value of create_tree?

I added

return new_tree;

If this is C, then both of these casts are unnecessary (as well as the one in create_tree):

Code:

    BNODE *root = (BNODE *)tree;
    if(root == 0){
        root = (BNODE *)malloc(sizeof(BNODE));

So what should I put instead?
Should I just declare the variable and not malloc it?

Originally Posted by Elysia

Mats is referring to that you should remove the casts, but it is not really necessary. The only problem is that it can hide some errors. But if you have a good compiler (like Visual C++), it will warn about it anyway.
There is nothing wrong with casts in the assignments, however (from void* to T*). You don't need it, but if you feel like having it, there's nothing wrong with that either.
I like having casts, myself.

So what do i do to fix my segfault........

PLease help me...

Despite your returning a node from create_tree() you are not initializing the name pointer as in

Code:

void *create_tree(){ /* root->name is not initialized in this routine */
    BNODE *new_tree = (BNODE *)malloc(sizeof(BNODE));
    new_tree->left = NULL;
    new_tree->right = NULL;

}

you allocated the root node but forgot to initialize its element root->name so what do you think will happen to strcmp()?