linked list - basic concept.

Hello, I started this week to deal a little bit with linked lists, I did a simple example, I'm not sure the way I did it is correct, maybe I'm missing something, here's the code:

Code:

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

struct node {
	int data;
	struct node *next; //wohhaaa... a linked list :)
};

void add( struct node **head, int data ) {
	struct node *tmp = malloc( sizeof ( struct node ) );
	
	tmp->data = data;
	tmp->next = *head;

	*head = tmp;
}

void print( struct node *head ) {
	struct node *current = head;
	
	while( current ) {
		printf( "data: %d\n", current->data );
		current = current->next;
	}
}

void collect( struct node *head ) {
	struct node *current = head;
	
	while(current ) {
		free( current );
		current = current->next;
	}
}

int main( void ) {
	struct node *head = NULL;

	add( &head, 4 );
	add( &head, 3 );
	add( &head, 2 );

	print( head );
	collect( head );
	return 0;
}

My big question is, my collect() function really works? it's correct, or I'm forgetting to free something?

my collect() function really works?

Nope, it's buggy and very dangerous. Why?

Code:

free( current );
current = current->next;

What makes you think that you can access a pointer that's already been freed? Just because it was freed the line before doesn't mean the memory hasn't been reused. A better way is to save the next pointer, then free the current pointer, then set the current pointer to the saved next pointer

Code:

void collect( struct node *head ) {
    struct node *current = head;
    struct node *forward;

    while(current ) {
        forward = current->next;
        free( current );
        current = forward;
    }
}

no its not correct. look

Code:

void collect( struct node *head ) {
	struct node *current = head;
	
	while(current ) {
		free( current ); // current is dead after this call
		current = current->next;// but you access it here.
	}
}

oops beaten

Ok, thanks for helping
Any other comments about my code? I'm still missing something?

I have altered your collect function, you should find the nodes are deleted correctly now

Code:

void collect( struct node *head ) {
	struct node *current = head;
	struct node *p;


	while(current){
		p = current->next;
		free( current );
		current = p;

		//check if node really is freed
		printf("\n\n Deleting node\n");
		print(current);

	}
}