Thread: Pointer confusion

Ok I'm getting slightly insane here.
Before I begin to ask my question I will give you some code:

Code:

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

#include "misc.h"

#define MAX_ANSWERS 3

typedef struct quest
{
        char question[100];
        char answer[MAX_ANSWERS][100];
        int  correct[MAX_ANSWERS];
        struct quest* next;
} QUEST;

void make_question(QUEST** q);
void make_quiz(QUEST** phead);

int main(void)
{
    QUEST* head = NULL;
    
    make_quiz(head);
    getchar();
    return 0;
}

void make_quiz(QUEST** phead)
{
     QUEST* q = NULL, *qprev = NULL;
     char newquest = 'j';
     int i=0;
     
     phead = malloc(sizeof(QUEST));
     
     while(newquest == 'j')
     {
         printf("*** Vraag %d\n-\n\n", ++i);
         make_question(q);
         printf("-> %s", q->question);
         if (qprev!=NULL)
            qprev->next = q;
         else
            phead = q;
         qprev = malloc(sizeof(QUEST));
         qprev = q;
         printf("Wil je nog een vraag toevoegen ? (j/n): ");
         scanf("%c", &newquest);
         fflush(stdin);
     }
     
}

void make_question(QUEST** pq)
{
     int i, correctgiven=0;
     char correct;
          
     pq = malloc(sizeof(QUEST));
     printf("Typ je vraag: ");
     scanf("%[^\n]%*c", &pq->question);
     fflush(stdin);
     
     for(i=1;i<=MAX_ANSWERS;i++)
     {
           printf("\nAntwoord %d: ", i);
           scanf("%[^\n]%*c", &pq->answer[i]);
           fflush(stdin);
           
           if (!correctgiven)
           {
              printf("Is dit antwoord correct ? (j/n)");
              scanf("%c", &correct);
              fflush(stdin);
              
              if (correct == 'j')
              {
                 correctgiven = 1; 
                 pq->correct[i] = 1;
              } else
                 pq->correct[i] = 0;
           }
     }
     &pq->next = NULL;
}

I want to build a linked list of QUEST's.
First I call make_quiz() wich calls make_question() in a loop.
I give "head" along with make_quiz (byval) wich has to assign an address to head. But it just doesn't work.

What am I doing wrong ?

you need to pass a pointer to the QUEST pointer, as shown below.

Code:

    QUEST* head = NULL;
    
    make_quiz(&head);

Then make_quiz need to dereference that pointer so that it can allocate memory to main()'s pointer.

Code:

void make_quiz(QUEST** phead)
{
    ...     
     *phead = malloc(sizeof(QUEST));

  ...
    (*pq)->next = NULL;

and do similar stuff in other functions

YES ! That did it thnx !

your program is writing the structures in binary format, so yes you will probably see a lot of trash in the file if you look at it with a normal text editor such as Notepad.exe.