Linked List pointers prob - c

Question

I do not know why this is not working.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
// struct of list
typedef struct noeud
{
int adresse, taille, temp;
struct noeud* suivant;
} * liste;
int random(int a, int b)
{
return (a + (rand() % ((b + 1) + a)));
}
void initialisation(liste* LBO)
{
*LBO = NULL;
}
I think it's here the problem when I create q (q is created to point to the previous node).
void creation(liste* LBO)
{
liste q, prec = NULL;
int i = 0;
srand(time(NULL));
while (i < 3)
{
printf("%d", i);
q = malloc(sizeof(liste));
if (*LBO == NULL)
{
q->adresse = 0;
q->taille = random(5, 45);
q->temp = random(5, 15);
q->suivant = *LBO;
*LBO = q;
i++;
}
else
{
prec = *LBO;
q->taille = random(5, 45);
q->temp = random(5, 15);
q->adresse = prec->adresse + prec->taille;
q->suivant = *LBO;
*LBO = q;
i++;
}
}
}
void affichage(liste LBO)
{
printf("\nvoici ta liste \n ");
while (LBO != NULL)
{
printf("%d-->", LBO->taille);
LBO = LBO->suivant;
}
if (LBO == NULL)
printf("NULL");
}
int main()
{
// or here
printf("Hello world!\n");
liste LBO;
initialisation(&LBO);
creation(&LBO);
affichage(LBO);
return 0;
}

Answer 1

There are several issues:
Instead of calling
initialisation(&LBO);
which is not really wrong, just write:
LBO = NULL;
Then don't hide pointers with typedefs, it only adds confusion.
Instead of:
typedef struct noeud
{
int adresse, taille, temp;
struct noeud* suivant;
} *liste;
Write:
struct noeud
{
int adresse, taille, temp;
struct noeud* suivant;
};
and use struct noeud* instead of liste.
Now the real problem:
This is wrong. Here you allocate the size for a pointer, but you need to allocate the size for the whole structure:
q = malloc(sizeof(liste));
which is actually the same as:
q = malloc(sizeof(struct noeud*))
but you need:
q = malloc(sizeof(struct noeud))
You see now why hiding pointers with typedefs is a bad idea.
So here is the corrected version of your program (#includes ommitted for brevity):
struct noeud
{
int adresse, taille, temp;
struct noeud* suivant;
};
int random(int a, int b)
{
return (a + (rand() % ((b + 1) + a)));
}
void creation(struct noeud** LBO)
{
struct noeud* q, *prec = NULL;
int i = 0;
// srand(time(NULL)); <<<<< don't call srand here, call it once at the
// beginning of the program
while (i < 3)
{
printf("%d", i);
q = malloc(sizeof(struct noeud));
if (*LBO == NULL)
{
q->adresse = 0;
q->taille = random(5, 45);
q->temp = random(5, 15);
q->suivant = *LBO;
*LBO = q;
i++;
}
else
{
prec = *LBO;
q->taille = random(5, 45);
q->temp = random(5, 15);
q->adresse = prec->adresse + prec->taille;
q->suivant = *LBO;
*LBO = q;
i++;
}
}
}
void affichage(struct noeud* LBO)
{
printf("\nvoici ta struct noeud* \n ");
while (LBO != NULL)
{
printf("%d-->", LBO->taille);
LBO = LBO->suivant;
}
// if (LBO == NULL) <<<<<<<<<<< drop this, LBO is always NULL here
// but it doesn't hurt, it's just useless
printf("NULL");
}
int main()
{
srand(time(NULL)); // <<<<<<<<<<<<< call srand here
struct noeud* LBO;
LBO = NULL;
creation(&LBO);
affichage(LBO);
return 0;
}
There is still room for improvement, especially the creation function is somewhat awkward.
Also look at the comments with <<<<<<<<<<<, there are minor corrections