Simple Singly Linked List Question - Node Values not displaying

Question

I'm a Noob, trying to build a singly linked linked list in C, based upon an array of strings (where the array can have different lengths and items are of different size). In the code I have modified, I seem to be getting the right number of pointers, but none of the Node values are displaying. Desired output to console is head --> one --> two --> etc. (right now, I'm just getting head --> --> -->)

// starter code from https://www.tutorialspoint.com/learn_c_by_examples/simple_linked_list_program_in_c.htm

#include <stdio.h>
#include <stdlib.h>

struct node {
    const char *data;
    struct node *next;
};

struct node *head = NULL;
struct node *current = NULL;

//display the list
void printList() {

    struct node *ptr = head;

    printf("\n[head] =>");
    //start from the beginning
    while(ptr != NULL) {  
        printf(" %s =>", ptr -> data);
        ptr = ptr -> next;
    }

    printf(" [null]\n");
}

//insert link at the first location
void insert(const char data) {
    //create a link
    struct node *link = (struct node*) malloc(sizeof(struct node));

    //link->key = key;
    link -> data = &data;

    //point it to old first node
    link -> next = head;

    //point first to new first node
    head = link;
    }

int main() {
    // create an array of strings, to be used to dynamically populate linked list
    const char *strings[] = {"one" ,"two","three", "four", "somewhereselse", "onemore"};

    // below line to find number of items in an array of strings, assign to n
    int n = sizeof(strings) / (2 * sizeof(int));

    for (int j = 0; j < n; j++){
        const char *temp = strings[j];
        insert(*temp);
        //printf("%s\n", temp);

    }

    printList();
    return 0;
}

Answer 1

try this code instead

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct node {
    char *data;
    struct node *next;
};

struct node *head = NULL;
struct node *current = NULL;

//display the list
void printList() {

    struct node *ptr = head;

    printf("\n[head] =>");
    //start from the beginning
    while(ptr != NULL) {  
        printf(" %s =>", ptr -> data);
        ptr = ptr -> next;
    }

    printf(" [null]\n");
}

//insert link at the first location
void insert(char *data) {
    //create a link
    struct node *link = (struct node*) malloc(sizeof(struct node));
link->data=malloc(strlen(data)*sizeof(char)); //don't forget malloc for string : link->data
    strcpy(link->data,data); //copy  parameter named data to link->data

    //point it to old first node
    link -> next = head;

    //point first to new first node
    head = link;

    }

int main() {
    // create an array of strings, to be used to dynamically populate linked list
    const char *strings[] = {"one" ,"two","three", "four", "somewhereselse", "onemore"};

    // below line to find number of items in an array of strings, assign to n
    int n = sizeof(strings) / (2 * sizeof(int));
    char temp[20]={0};
    for (int j =n-1; j >=0; j--){
        //const char *temp = strings[j];
        strcpy(temp,strings[j]);
        insert(temp);
        //printf("%s\n", temp);

    }

    printList();
    return 0;
}

Answer 2

My code did not work due to 3 pieces of syntax, which I have identified below

// starter code from https://www.tutorialspoint.com/learn_c_by_examples/simple_linked_list_program_in_c.htm

#include <stdio.h>
#include <stdlib.h>

struct node {
    const char *data;
    struct node *next;
};

struct node *head = NULL;
struct node *current = NULL;

//display the list
void printList() {

    struct node *ptr = head;

    printf("\n[head] =>");
    //start from the beginning
    while(ptr != NULL) {  
        printf(" %s =>", ptr -> data);
        ptr = ptr -> next;
    }

    printf(" [null]\n");
}

//insert link at the first location
// first change insert *
void insert(const char *data) {
    //create a link
    struct node *link = (struct node*) malloc(sizeof(struct node));

    //link->key = key;
    // 2nd change remove &
    link -> data = data;

    //point it to old first node
    link -> next = head;

    //point first to new first node
    head = link;
    }

int main() {
    // create an array of strings, to be used to dynamically populate linked list
    const char *strings[] = {"one" ,"two","three", "four", "somewhereselse", "onemore"};

    // below line to find number of items in an array of strings, assign to n
    int n = sizeof(strings) / (2 * sizeof(int));

    for (int j = 0; j < n; j++){
        const char *temp = strings[j];
        // 3rd change remove * before temp
        insert(temp);
        //printf("%s\n", temp);

    }

    printList();
    return 0;
}

Answer 3

void insert(const char data) 

This is wrong.

You're inserting a single character. Well, specifically, you're inserting a pointer to this single character:

link -> data = &data;

...but (a) that character's on the stack, so the pointer's not going to stay valid for very long, and (b) it's not the string that you think it is.

This:

insert(*temp);

Should be:

insert(temp);

...and you should change the prototypes and implementation to match.

Note also that you might want to take a copy of the string (use strdup, but be aware of memory leaks), rather than point to the original one.