Explain generic linked list in C - c

Question

Kindly explain push function. I could not get why loop is used . For char and int (new_node->data=new_data) works fine . But for string , it doesn't . For string , error is produced. If char(%c) is printed for new_data in push() method then only first character is printed , while if char(%c) is printed for new_node->data then last characater is printed.
// C program for generic linked list
#include<stdio.h>
#include<stdlib.h>
/* A linked list node */
struct node
{
// Any data type can be stored in this node
void *data;
struct node *next;
};
/* Function to add a node at the beginning of Linked List.
This function expects a pointer to the data to be added
and size of the data type */
void push(struct node** head_ref, void *new_data, size_t data_size)
{
// Allocate memory for node
struct node* new_node = (struct node*)malloc(sizeof(struct node));
new_node->data = malloc(data_size);
new_node->next = (*head_ref);
// Copy contents of new_data to newly allocated memory.
// Assumption: char takes 1 byte.
int i;
//Why loop is used for copying data from new_data to new_node data.
for (i=0; i<data_size; i++)
*(char *)(new_node->data + i) = *(char *)(new_data + i);
// Change head pointer as new node is added at the beginning
(*head_ref) = new_node;
}
/* Function to print nodes in a given linked list. fpitr is used
to access the function to be used for printing current node data.
Note that different data types need different specifier in printf() */
void printList(struct node *node, void (*fptr)(void *))
{
while (node != NULL)
{
(*fptr)(node->data);
node = node->next;
}
}
// Function to print an integer
void printInt(void *n)
{
printf(" %d", *(int *)n);
}
// Function to print a float
void printFloat(void *f)
{
printf(" %f", *(float *)f);
}
/* Driver program to test above function */
int main()
{
struct node *start = NULL;
// Create and print an int linked list
unsigned int_size = sizeof(int);
int arr[] = {10, 20, 30, 40, 50}, i;
for (i=4; i>=0; i--)
push(&start, &arr[i], int_size);
printf("Created integer linked list is \n");
printList(start, printInt);
// Create and print a float linked list
unsigned float_size = sizeof(float);
start = NULL;
float arr2[] = {10.1, 20.2, 30.3, 40.4, 50.5};
for (i=4; i>=0; i--)
push(&start, &arr2[i], float_size);
printf("\n\nCreated float linked list is \n");
printList(start, printFloat);
return 0;
}

Answer 1

yes , we can also do new_node->data=new_data instead of using this loop
for (i=0; i<data_size; i++)
*(char *)(new_node->data + i) = *(char *)(new_data + i);
but there is difference between them. when we simply using new_node->data=new_data we are shallow copying.therefore two pointers pointing to the same location i.e if you change the values of arr[] then automatically the values in the struct changes.
when you using loop you are deep copying i.e if you change the values of the arr[] then the values of the struct will not get changed.
run the below code to understand the differnce.
// C program for showing shallow copy in generic linked list
#include<stdio.h>
#include<stdlib.h>
/* A linked list node */
struct Node
{
// Any data type can be stored in this node
void *data;
struct Node *next;
};
/* Function to add a node at the beginning of Linked List.
This function expects a pointer to the data to be added
and size of the data type */
void push(struct Node** head_ref, void *new_data, size_t data_size)
{
// Allocate memory for node
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = malloc(data_size);
new_node->next = (*head_ref);
// Copy contents of new_data to newly allocated memory.
// Assumption: char takes 1 byte.
int i;
// no loop just normal assignment of new_data
new_node->data=new_data;
printf("\n");
// Change head pointer as new node is added at the beginning
(*head_ref) = new_node;
}
/* Function to print nodes in a given linked list. fpitr is used
to access the function to be used for printing current node data.
Note that different data types need different specifier in printf() */
void printList(struct Node *node, void (*fptr)(void *))
{
while (node != NULL)
{
(*fptr)(node->data);
node = node->next;
}
}
// Function to print an integer
void printInt(void *n)
{
printf(" %d", *(int *)n);
}
// Function to print a float
void printFloat(void *f)
{
printf(" %f", *(float *)f);
}
/* Driver program to test above function */
int main()
{
struct Node *start = NULL;
// Create and print an int linked list
unsigned int_size = sizeof(int);
int arr[] = {1,2,3,4,5}, i;
for (i=4; i>=0; i--)
push(&start, &arr[i], int_size);
printf("Created integer linked list is \n");
printList(start, printInt);
printf("\n");
// changing the values in arr[]
arr[1]=45;
arr[3]=1000;
//printing the struct
printf("printing the struct after changing the values in the array \n");
printList(start, printInt);
/*
// Create and print a float linked list
unsigned float_size = sizeof(float);
start = NULL;
float arr2[] = {10.1, 20.2, 30.3, 40.4, 50.5};
for (i=4; i>=0; i--)
push(&start, &arr2[i], float_size);
printf("\n\nCreated float linked list is \n");
printList(start, printFloat);*/
return 0;
}