Malloc error while inserting an element in a red black tree

Question

#include<stdio.h>
#include<stdlib.h>
typedef struct treenode{
    int elem;
    int color;
    struct treenode *left,*right,*parent;
}treenode_t;
treenode_t *create_node(int elem){
    treenode_t *newnode=(treenode_t *)malloc(sizeof(treenode_t *));
    newnode->elem=elem;
    newnode->left=NULL;
    newnode->right=NULL;
    newnode->color=0;
    newnode->parent=NULL;
    return newnode;
}
void insert(treenode_t **node,int elem){
    if(*node==NULL){
        *node=create_node(elem);
    }else{
        treenode_t *store_parent;
        treenode_t *ptr;
        ptr=*node;
        while(ptr!=NULL){
            store_parent=ptr;
            if(elem<ptr->elem){
                if(ptr->left==NULL){
                    ptr->left=create_node(elem);
                    (ptr->left)->parent=store_parent;
                    (ptr->left)->color=1;
                }
                ptr=ptr->left;
            }
            else if(elem>ptr->elem){
                if(ptr->right==NULL){
                ptr->right=create_node(elem);
                (ptr->right)->parent=store_parent;
                (ptr->right)->color=1;
                }
                ptr=ptr->right;
            }
        }
    }
}
void print_tree(treenode_t *node){
    if(node==NULL)
        return;
    print_tree(node->left);
    printf("%d\n",node->elem);
    print_tree(node->right);
}
void main(){
    treenode_t *root=NULL;
    insert(&root,10);
    insert(&root,5);
    insert(&root,14);
    print_tree(root);
}

I am able to insert the first element but the second time the malloc fails.

Using GDB: When i use gdb i found that once i have created the first node(the root of the tree), when i go insert the second element i.e. 5 the line ptr->left=create_node(elem) redirects to the function create_node().The address which is allocated to malloc is the same as that is stored in the root which results in the error.

I get the following error:

a.out: malloc.c:2372: sysmalloc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 *(sizeof(size_t))) - 1)) & ~((2 *(sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && ((unsigned long) old_end & pagemask) == 0)' failed.

Program received signal SIGABRT, Aborted. 0x00007ffff7a4af79 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 56 ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.

Now do i have to change the address the of the memory that is allocated by malloc(if so,how?) or is there some other problem in the code?

Jeff Kelley Jeff Kelley · Accepted Answer · 2016-02-06T15:53:08

I think the problem is the parameter you’re using to call malloc with:

treenode_t *newnode=(treenode_t *)malloc(sizeof(treenode_t *));

You’re asking for memory, but I don’t think you’re asking for enough. sizeof(treenode_t *) returns the size of a pointer to a treenode_t; what you need is enough space for the entire struct. Try using sizeof(treenode_t) instead and see if that helps.

Malloc error while inserting an element in a red black tree

1 Answers