Making a cpnode function? - c

Question

I am trying to make a function that copies a node. I am trying to have the program on error or NULL return NULL, I can only have one return statement
I have the following code and I am not sure what else to do from here.. Any tips/advice I would greatly appreciate
Node *cpnode(Node *curNode)
{
if (curNode == NULL) return NULL;
Node *result = malloc(sizeof *result);
result -> value = curNode -> value;
result -> next = cpnode(curNode -> next;
return(result);
}
EDIT:
I have edited my code when trying to compile I am getting errors such as
Node has no member named 'value' and 'next'. Why is that?
Also I know I can easily return NULL on my if statement and at the end return with my result but how could I just have only one return statement with NULL on error?
To define my Node would I have to do something like this:
Node *cpnode(Node *curNode)
{
struct Node{
*result;
*value;
*next;
}
if (curNode == NULL) return NULL;
Node *result = malloc(sizeof *result);
result -> value = curNode -> value;
result -> next = cpnode(curNode -> next;
return(result);
}

Answer 1

There are several issues with your code: your Node structure isn't properly defined and you're using it as a type which you didn't typedef; your text talks about copying a node but your code copies a linked list of nodes; result doesn't seem like it should be part of the Node structure; your code isn't syntactically correct (e.g. missing paren).
Here's a rework of your code into something that compiles and runs. Since you didn't specify the type for value, I'm assuming it's a string below but you can change that to whatever you want:
#include <stdlib.h>
#include <stdio.h>
typedef struct Node
{
char *value;
struct Node *next;
} Node;
Node *copyNodes(Node *currentNode)
{
Node *result = NULL;
if (currentNode != NULL)
{
if ((result = malloc(sizeof *result)) != NULL)
{
result->value = currentNode->value;
result->next = copyNodes(currentNode->next);
}
}
return result;
}
void freeNodes(Node *currentNode)
{
if (currentNode != NULL)
{
if (currentNode->next != NULL)
{
freeNodes(currentNode->next);
currentNode->next = NULL;
}
}
free(currentNode);
}
int main()
{
Node a, b;
b.value = "last";
b.next = NULL;
a.value = "first";
a.next = &b;
Node *c = copyNodes(&a);
printf("%s\n", c->next->value);
freeNodes(c);
return 0;
}
If we make a copy of all the nodes using malloc(), then when finished, we need to free all the copies in a similar fashion to how they were created. That's what the function freeNodes() does.