Trouble in insertion of string in linked list - c

Question

I am writing a program to insert data to linked list and print it.
LinkedList.c
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
struct node
{
char *data;
struct node *next;
};
void insert(struct node** head_ref,char *new_data)
{
struct node* new_node = (struct node*) malloc(sizeof(struct node));
struct node *last = *head_ref;
strcpy(new_node->data,new_data);
new_node->next = NULL;
if (*head_ref == NULL)
{
*head_ref = new_node;//assigning head node
return;
}
while (last->next != NULL)
last = last->next;//this helps to traverse to last node
last->next = new_node;
return;
}
void printList(struct node *node)//function to print the linked list
{
while (node != NULL)
{
printf(" %s ", node->data);
node = node->next;
}
}
int main() {
int t;
char datas[1000];
scanf("%d",&t);
struct node* head=NULL;
int i;
for(i=0;i<t;i++)
{
scanf("%s",datas);//this data should be added into the linkedlist
insert(&head,datas);
}
printList(head);
return 0;
}
This program works well for integer but if i use character string instead it showing that there is no response on stdout
I have been trying to debug the code for more hours.

Answer 1

Your code gives undefined behavior.
Have a look at the documentation of strcpy().
Long story short, strcpy() requires the destination (your new_node->data) to be an allocated char array, but you have not allocated the data for it, and you are writing to an undefined (and unallocated) memory.
To overcome it, either allocate space dynamically for the new string (and don't forget to free it when a node is released), or make data a char[] instead of a char*.
In addition, just remember buffer overflow weakness. Since it seems like educational purpose code, just think about it - don't try to solve it, IMO.

Answer 2

You have missed memory allocation, try this:
void insert(struct node** head_ref,char *new_data)
{
struct node* new_node = (struct node*) malloc(sizeof(struct node));
struct node *last = *head_ref;
// you should allocate memory because you use data as char *
new_node->data = malloc(strlen(new_data)+1);
/* you can use new_node->data = strdup(new_data);
instead of new_node->data = malloc(strlen(new_data)); and strcpy(new_node->data,new_data);
because strdup allocate and copy string with exact size */
strcpy(new_node->data,new_data);
new_node->next = NULL;
if (*head_ref == NULL)
{
*head_ref = new_node;//assigning head node
return;
}
while (last->next != NULL)
last = last->next;//this helps to traverse to last node
last->next = new_node;
return;
}