creating a binary search tree with strings

Question

#include<stdio.h>    
#include<conio.h>
#include<malloc.h>
#include<string.h>

struct node{
    char *name;
    struct node *lchild;
    struct node *rchild;
}*root;


void find(char *str,struct node **par,struct node **loc)
{
    struct node *ptr,*ptrsave;
    if(root==NULL)
    {
        *loc=NULL;
        *par=NULL;
        return;
    }
    if(!(strcmp(str,root->name)))
    {
        *loc=root;
        *par=NULL;
        return;
    }
    if(strcmp(str,root->name)<0)
        ptr=root->lchild;
    else
        ptr=root->rchild;
    ptrsave=root;
    while(ptr!=NULL)
    {
        if(!(strcmp(str,ptr->name)))
        {
            *loc=ptr;
            *par=ptrsave;
            return;
        }
        ptrsave=ptr;
        if(strcmp(str,ptr->name)<0)
            ptr=ptr->lchild;
        else
            ptr=ptr->rchild;
    }
    *loc=NULL;
    *par=ptrsave;
}


void insert(char *str)
{
    struct node *parent,*location,*temp;
    find(str,&parent,&location);
    if(location!=NULL)
    {
        printf("Name already present\n");
        return;
    }
    temp=(struct node*)malloc(sizeof(struct node));
    temp->name=str;
    temp->lchild=NULL;
    temp->rchild=NULL;
    if(parent==NULL)
        root=temp;
    else
        if(strcmp(str,parent->name)<0)
            parent->lchild=temp;
        else
            parent->rchild=temp;
}


void displayin(struct node *ptr)
{
    if(root==NULL)
    {
        printf("Tree is empty");
        return;
    }
    if(ptr!=NULL)
    {
        displayin(ptr->lchild);
        printf("%s -> ",ptr->name);
        displayin(ptr->rchild);
    }
}


int main()
{
    root=NULL;
    char str[20];
    while(1)
    {
        printf("Enter name: ");
        fflush(stdin);
        gets(str);
        insert(str);
        printf("Wants to insert more item: ");
        if(getchar()=='y')
        insert(str);
        else
        break;
    }
    displayin(root);
    getch();
    getchar();
    return 0;
 }

If i run this piece of code with following input

rakesh rajesh bimal

then,it is displaying the output as "bimal->" which is wrong. I don't know where the logic is going wrong. I crosschecked but not able to find mistake. Can somebody take a look on this.

Answer 1

One of the issue:

In your insert() function you are doing

temp=(struct node*)malloc(sizeof(struct node));
temp->name=str; //this is not correct, 

//do 
temp=malloc(sizeof(struct node)); // no type cast for malloc
temp->name = strdup(str);         //allocate memory too
//also check you NULL and free the allocated memory.

Your are just setting the pointer location in the node you created for string to store, but it points to str array from main() . So all nodes will point to same location, which will have last value entered. In your case its "bimal" .

Answer 2

Your find function is in any case quite obscure. This is the improved version.

void find(char *str,struct node **par,struct node **loc)
{
    *par = NULL;
    *loc = NULL;
    struct node *ptr,*ptrsave;
    if(root==NULL) return;
    if(!(strcmp(str,root->name)))
    {
        *loc=root;
        return;
    }
    ptrsave = NULL;
    ptr = root;
    while(ptr!=NULL) {
        if(!(strcmp(str,ptr->name))) break;
        ptrsave = ptr;
        if(strcmp(str,ptr->name)<0)
            ptr=ptr->lchild;
        else
            ptr=ptr->rchild;
    }
    *loc=ptr;
    *par=ptrsave;
}