Delete element from doubly linked list using recursive - c

Question

I want to delete an element from doubly linked list, but i need to using recursion.
I write function but it doesn't work. Can someone tell me where did i a mistake?
int deleteNode(struct dll_node **front, int data){
if((*front) == NULL){
return 0;
}
if(data == (*front)->data){
int tmp = (*front)->data;
(*front)->next = (*front)->prev;
(*front)->prev = (*front)->next;
free(*front);
return tmp;
}
deleteNode((*front)->next, data);
}

Answer 1

there are several problems
you save data in tmp for nothing
you do not update rightly the list
your recursive call does not give right the first argument (must be deleteNode(&(*front)->next, data);, and in fact you must return it), note it is terminal so you can also use a loop
return is missing if the two tests are false
It can be :
int deleteNode(struct dll_node **front, int data){
if((*front) == NULL){
return 0;
}
if(data == (*front)->data){
struct dll_node * d = *front;
if (d->prev == NULL) {
if ((*front = d->next) != NULL)
(*front)->prev = NULL;
}
else if ((d->prev->next = d->next) != NULL)
d->next->prev = d->prev;
free(d);
return data;
}
return deleteNode(&(*front)->next, data);
}
Full code to check :
#include <stdio.h>
#include <stdlib.h>
struct dll_node {
int data;
struct dll_node * prev;
struct dll_node * next;
};
int deleteNode(struct dll_node **front, int data){
if((*front) == NULL){
return 0;
}
if(data == (*front)->data){
struct dll_node * d = *front;
if (d->prev == NULL) {
if ((*front = d->next) != NULL)
(*front)->prev = NULL;
}
else if ((d->prev->next = d->next) != NULL)
d->next->prev = d->prev;
free(d);
return data;
}
return deleteNode(&(*front)->next, data);
}
struct dll_node * mk(int d)
{
struct dll_node * r = malloc(sizeof(struct dll_node));
r->data = d;
r->prev = NULL;
r->next = NULL;
return r;
}
void pr(struct dll_node * l)
{
while (l != NULL) {
printf("%d", l->data);
if (l->prev)
printf(" prev:%d\n", l->prev->data);
else
putchar('\n');
l = l->next;
}
}
int main()
{
struct dll_node * head = mk(1);
struct dll_node * a = mk(2);
struct dll_node * b = mk(3);
head->next = a;
a->prev = head;
b->prev = a;
a->next = b;
pr(head);
puts("\ndel 3");
deleteNode(&head, 3);
pr(head);
puts("\ndel 1");
deleteNode(&head, 1);
pr(head);
puts("\ndel 2");
deleteNode(&head, 2);
pr(head);
}
Compilation and executions :
pi#raspberrypi:/tmp $ gcc -Wall l.c
pi#raspberrypi:/tmp $ ./a.out
1
2 prev:1
3 prev:2
del 3
1
2 prev:1
del 1
2
del 2
pi#raspberrypi:/tmp $ valgrind ./a.out
==8496== Memcheck, a memory error detector
==8496== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==8496== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==8496== Command: ./a.out
==8496==
1
2 prev:1
3 prev:2
del 3
1
2 prev:1
del 1
2
del 2
==8496==
==8496== HEAP SUMMARY:
==8496== in use at exit: 0 bytes in 0 blocks
==8496== total heap usage: 4 allocs, 4 frees, 1,060 bytes allocated
==8496==
==8496== All heap blocks were freed -- no leaks are possible
==8496==
==8496== For lists of detected and suppressed errors, rerun with: -s
==8496== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
pi#raspberrypi:/tmp $