Why I get this wrong output? - c

Question

I created this simple double linked list.
The problem is that when I print all its elements, they have the same char value even if the variable "a" changes every time.
typedef struct node{
char *name;
struct node *n;
struct node *p;
} N;
N *h=NULL;//head
void insert(char *value){
N *temp=malloc(sizeof(N));
if(h==NULL){
h=temp;
temp->name=strdup(value);
}
else{
N *curr=h;
while(curr->n!=NULL)
curr=curr->n;
curr->n=temp;
temp->p=curr;
temp->name=strdup(value);
}
}
void print(){
N *temp=h;
printf("%s\n", temp->name);
while(temp->n!=NULL){
printf("%s\n", temp->name);
temp=temp->n;
}
}
int main(){
char a[...];
fgets(a,...)
//there is a while section: every time i enter in it, there is:
char *input=a;
insert(input);
print();
}
So I expected something as:
Lion
Bear
Goat
....
Instead i get:
Lion, then
Bear
Bear, then
Goat
Goat
Goat
etc...

Answer 1

There are a couple of issues. First you have a bug in print() that prevents the last value from being displayed. Check temp instead of temp->n:
void print()
{
N *temp=h;
while(temp !=NULL){
printf("%s\n", temp->name);
temp=temp->n;
}
}
Your extra printf() call (before the while loop) is why the first value was printed twice.
Also you must assign p and n when you add a new node. You can't assume that they will be NULL if you don't assign them.
void insert(char *value)
{
N *temp=malloc(sizeof(N));
if(h==NULL){
h=temp;
temp->p = NULL;
temp->n = NULL;
temp->name=strdup(value);
}
else{
N *curr=h;
while(curr->n!=NULL)
curr=curr->n;
curr->n=temp;
temp->p=curr;
temp->n = NULL;
temp->name=strdup(value);
}
}
Also, do you need the list to be double-linked? You never use the p pointer.

Answer 2

You're pointing to the same memory for each list element. This code
temp->name=value;
merely copies the value of the pointer to temp->name because of the definition of the structure:
typedef struct node{
char *name;
struct node *n;
struct node *p;
} N;
name is just a pointer. You need to duplicate the string that value points to, not just point name at value (input validation and error checking are left as an exercise for the reader...):
char *duplicateString( const char *inputString )
{
char newString = malloc( strlen( inputString ) + 1 );
strcpy( newString, inputString );
return( newString );
}
so
temp->name = duplicateString( value );
Just remember to call free( temp->name ) before you call free( temp ) to free your node.
or just use strdup() if you're on a POSIX system:
temp->name = strdup( value );