Difference between char, char* inside Linked Lists - c

Question

I created a linked list that hold int and char type data. A function adds the data to the list and the other prints it out. When i only print the int type i get no problems but when i try to also print the char type the program crashes.
So it has to do the way i'm defining the char* in the printing function print_list().
To be more specific my problem is here in print_list() :
printf("\n [%s] \n", ptr -> name);
printf("\n [%s] \n", ptr -> lastn);
So my actual code is (getting 0 errors and 0 warnings but the program crashes):
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
// Creating structure for node
struct test_struct
{
int val; // val is member id number
char name;
char lastn;
int age;
struct test_struct *next;
};
// declaring global head and curr pointers
struct test_struct *head = NULL;
struct test_struct *curr = NULL;
// creating a list
struct test_struct* create_list(int val, char* name, char* lastn, int age)
{
printf("\n creating list with head node as [%d] [%s] [%s] [%d] \n", val, name, lastn, age);
struct test_struct *ptr = malloc(sizeof(struct test_struct)); // creating list
if(NULL == ptr) {
printf("\n Node creation failed \n");
return NULL;
}
ptr->val = val;
ptr->name = *name;
ptr->lastn = *lastn;
ptr->age = age;
ptr->next = NULL;
head = curr = ptr;
return ptr;
}
// add member to list
struct test_struct* add_to_list(int val, char *name, char *lastn, int age, bool add_to_end)
{
if(NULL == head) {
return (create_list(val, name, lastn, age));
}
if(add_to_end) {
printf("\n Adding node to end of list with data [%d] [%s] [%s] [%d] \n", val, name, lastn, age);
} else {
printf("\n Adding node to beginning of list with data [%d] [%s] [%s] [%d] \n", val, name, lastn, age);
}
struct test_struct *ptr = malloc(sizeof(struct test_struct));
if(NULL == ptr) {
printf("\n Node creation failed \n");
return NULL;
}
ptr->val = val;
ptr->name = *name;
ptr->lastn = *lastn;
ptr->age = age;
ptr->next = NULL;
if (add_to_end) {
curr-> next = ptr;
curr = ptr;
} else {
ptr -> next = head;
head = ptr;
}
return ptr;
}
//printing the list
void print_list(void)
{
struct test_struct *ptr = head;
printf("\n -----Printing list Start----- \n");
while(ptr != NULL) {
printf("\n [%d] \n", ptr -> val);
printf("\n [%s] \n", ptr -> name);
printf("\n [%s] \n", ptr -> lastn);
printf("\n [%d] \n", ptr -> age);
ptr = ptr->next;
}
printf("\n -----Printing list end---- \n");
return;
}
// main function
int main(void)
{
struct test_struct *ptr = NULL;
// for adding member to list
add_to_list(123, "william", "shakespeare", 30, true);
add_to_list(124, "william", "gibson", 35, true);
add_to_list(125, "chuck", "palahniuk", 40, true);
add_to_list(126, "mario", "puzio", 50, true);
add_to_list(127, "umberto", "eco", 60, true);
add_to_list(128, "ezra", "pound", 125, true);
print_list();
return 0;
}

Answer 1

You have declared name and lastn as single characters
struct test_struct
{
int val; // val is member id number
char name;
char lastn;
int age;
struct test_struct *next;
};
you need to declare them either as fixed size arrays or pointers which point to allocated space to hold the strings. A string is a series of characters terminated by a \0.
struct test_struct
{
int val; // val is member id number
char name[MAXLEN];
char lastn[MAXLEN];
int age;
struct test_struct *next;
};
then copy arguments to the function to the fields in the struct
e.g.
strcpy(ptr->name,name);
strcpy(ptr->lastn,lastn);

Answer 2

printf("\n [%s] \n", ptr -> name);
printf("\n [%s] \n", ptr -> lastn);
%s expects char * not char as both name and lastn are char variables.
And to store name and last name of a person you should prefer char array as single char variable can't store it . Therefore , declare them as char arrays .
Example -
struct test_struct
{
int val; // val is member id number
char name[20]; // or any desired length to store a name
char lastn[20]; // similar as for name
int age;
struct test_struct *next;
};
And then to copy data in it use strncpy-
ptr->name = *name; // strncpy(ptr->name,name,strlen(name));
ptr->lastn = *lastn; // strncpy(ptr->lastn,lastn,strlen(lastn));