Printing struct from linked list
 

I have a linked list of structs, with each struct having a char* and an int.
When I try to print the list I get a seg fault. If I just print the int however it works. What am I doing wrong so the char* won't print?

printf("%s %d\n", p->name, p->age);

Thanks.

Re: Printing struct from linked list
 

A segmentation fault occurs when a program tries to access memory location that is not allow to play with.

My guess is that your char* is pointing to some wrong memory location. Maybe you haven't initialized to point to a string.

Re: Printing struct from linked list
 

After many tries I still have not figured out the problem. I no longer have a seg fault, but now when I try to print the list I get "garbage" values for the strings and the correct values for the ints. I have no idea why I am getting correct values for ints and not char *. Any ideas?

//mp3.h



#include <stdio.h>

#include <stdlib.h>

#include <string.h>



struct node

{

  char* artist;

  char* album;

  char* song;

  int date; //date the song is stored in the database

  int time; //in seconds

  int bitrate; //in kbps

  struct node* link;

};





void addToList(struct node **q);

void deleteFromList(struct node **q);

void printList(struct node *q);

//mp3.c



#include "mp3.h"





int main(void)

{

  struct node *p;

  p = NULL; //so p is the head of an empty list

  int choice=4;



  

  while(choice != 0)

    {

      printf("0: Exit.\n");

      printf("1: Add to the list.\n");

      printf("2: Delete from the list.\n");

      printf("3: Print the list.\n");

      scanf("%d", &choice);

      

      switch(choice)

        {

        case 1:

          addToList(&p);

          break;

        case 2:

          deleteFromList(&p);

          break;

        case 3:

          printList(p);

          break;

        default:

          break;

        }

      

    }

  

  return 0;

}



void addToList(struct node** q)

{

  struct node *temp;

  temp=(struct node *)malloc(sizeof(struct node));

  char tempString[80];



  //this is the 4-line version that works

  /*

  printf("Enter a name: ");

  scanf("%s", &tempString);

  temp->artist = tempString;

  printf("%s", temp->artist);

  */



  

  printf("Enter the name of the artist.\n");

  scanf("%s", &tempString);

  temp->artist = tempString;



  printf("Enter the name of the album.\n");

  scanf("%s", &tempString);

  temp->album = tempString;

  printf("Enter the name of the song.\n");

  scanf("%s", &tempString);

  temp->song = tempString;

  printf("Enter the date (mmddyyyy).\n");

  scanf("%d", &temp->date);

  printf("Enter the length of the song (in seconds).\n");

  scanf("%d", &temp->time);

  printf("Enter the quality (bitrate) of the song.\n");

  scanf("%d", &temp->bitrate);





  temp->link = *q;

  *q = temp;

}



void deleteFromList(struct node** q)

{



  

}



void printList(struct node* q)

{

  

  if(q == NULL)

    {

      printf("\n\nNo data.\n\n");

    }

  else

    {

      printf("\n\n Artist Name | Album Name | Song Name | Entry Date | Length | Quality\n");

      printf("----------------------------------------------------------------------\n");

      while(q != NULL)

        {

          printf("  %11s   %10s   %9s   %10d    %6d    %7d \n",q->artist,q->album,q->song,q->date,q->time,q->bitrate);

          q = q->link;

        }

    }

  

}

Thanks.

Re: Printing struct from linked list
 

Consider this:

  scanf("%s", &tempString);

  temp->artist = tempString;

The second argument to [icode]scanf[icode] is of the wrong type.

temp->artist

is a dangling pointer -- you need to allocate memory for it.
You don't copy the string with assignment, look into

strcpy

.

Re: Printing struct from linked list
 

Thanks for the response. I tried strcpy before, but that lead me to a seg fault. I'm sorry, how would I go about allocating memory for the pointer?

Re: Printing struct from linked list
 

Either make them arrays in the structure, or after you've read a string into tempString,

malloc(strlen(tempString)+1)

to the pointer.

Re: Printing struct from linked list
 

  scanf("%s", &tempString);

  strcpy(temp->artist, tempString);

  temp->artist = (char*) malloc(strlen(tempString)+1);

Is this what you mean?

I would make them arrays in the structure but the assignment specifies that they have to be char*s.

Re: Printing struct from linked list
 

Remove the & operator, tempString as such must be used in that scanf (tempString is a pointer, hence no need for &).

scanf("%s", &tempString);

Then allocate memory before copying.

temp->artist = (char*) malloc(strlen(tempString)+1);

strcpy(temp->artist, tempString);

You may want to check that malloc() actually succeeded, (i.e NULL != temp->artist). Also remember to free() all the malloc'ed memory at some point.

Re: Printing struct from linked list
 

Thank you so much mitrmkar - problem solved.