Losing elements while printing a queue in C - c

Question

This is my code :
typedef struct noeud{
int x;
struct noeud* suivant;
} noeud;
typedef noeud* file;
file enfiler(file f, int val){
file nv = (file) malloc(sizeof(noeud));
nv->x = val; nv->suivant = NULL;
if (f == NULL)
f = nv;
else {
file tmp = f;
while(tmp->suivant != NULL) tmp = tmp->suivant;
tmp->suivant = nv;
}
return f;
}
file defiler(file f){//removing an element of the FIFO data structure
if (f == NULL)
return f;
else {
file tmp = f;
f = f->suivant;//receiving address of next node, the last one points to NULL
free(tmp);
return f;
}
}
int tete(file f){
return f->x;//getting the element of the head
}
void init(file * f) {
*f = NULL;
}
void affiche(file f){//print data structure's elements
if (f == NULL)
printf("File vide.\n");
else {//emptying the FIFO data structure into tmp to access elements
file tmp; init(&tmp);
while(f != NULL){
tmp = enfiler(tmp, tete(f));
f = defiler(f);
}
int i = 0;
while(tmp != NULL) {//emptying tmp to original f
printf("F[%d] = %d\n", ++i, tete(tmp));
f = enfiler(f, tete(tmp));
tmp = defiler(tmp);
}
}
}
This is my input :
file f; init(&f);//initializing f to NULL
f = enfiler(f, 6);//adding elements
f = enfiler(f, 45);
f = enfiler(f, 78);
f = enfiler(f, 5);
affiche(f);
affiche(f);
affiche(f);
This is the output :
F[1] = 6
F[2] = 45
F[3] = 78
F[4] = 5
F[1] = 78
F[2] = 5
F[1] = 2036736 //this is a random value
With each void affiche(file f) two heads are being lost, I revised the function file defiler(file f) but can't seem to find an error, file enfiler(file f, int x) is also fine.
Thank you for your time!

Answer 1

In order to reverse the output, you construct and re-construct your queue. Your reconstruction does not re-link the same nodes. Instead, you just take the values and create two completely new lists. That means that the local variable f in afficher will usually be different when after entering and before leaving afficher. You can test that by adding the following statements:
void affiche(noeud *f)
{
printf("entree: %p\n", f);
// body of afficher function
printf("sortie: %p\n", f);
}
The problem is that the f in your calling function is not updated. It could point to recently free'd memory or to another valid node. In other words, your list will likely be corrupt.
The easiest way to fix that is by returning the new head, as in enfiler and defiler.