Segmentation fault in code for finding (inorder) successor of nodes in binary tree

Question

I was trying to find/print the inorder successor of each node in a binary tree but the compiler is giving me segmentation fault as the result.

Here is the structure:-

struct node
{
    int x;
    struct node *left;
    struct node *right;
};

Initial condition:

I've passed root of the tree as a (in succ() ) and NULL pointer as b .

Here is my code for printing/finding the successor:

struct node *(succ(struct node *a,struct node *b))
{
    struct node *xptr;
    xptr=b;                                                                     
    if(a!=NULL) 
    {                   
        xptr=succ(a->left,xptr);
        if(xptr!=NULL)          
        {                               
            printf(" %d is the successor of %d\n",a->x,xptr->x);
        }
        else                            
            printf("%d is the successor of no one\n",xptr->x);
        xptr=a;                         
        if(xptr->right==NULL)
        {                       
            return xptr;        
        }                               
        xptr=succ(a->right,xptr);               
        return xptr;                    
    }
    else                        
        return xptr; 
}

I've tested the rest of the code (building the tree) and it is working fine.

Answer 1

Consider this snippet:

if(xptr!=NULL)          
    {                               
        printf(" %d is the successor of %d\n",a->x,xptr->x);
    }
else                            
        printf("%d is the scuccessor of no one\n",xptr->x);

whenever the xptr is null , control enters else part and then tries to print xptr->x which is de-referencing a null pointer ( null->x ). Hence the segmentation fault.

I think you wrote this by mistake:

printf("%d is the successor of no one\n",xptr->x);

which in my opinion should be:

printf("%d is the successor of no one\n",a->x);