Thread: Basic linked list help

st is an instance of the Stack struct. However, all that struct contains is a pointer to struct node. There's no actual memory allocated for that one. To use that code you'd do something like this:

Code:

{
  Stack st;

  st.stack = malloc(sizeof(Node));
  st.stack->data = 86;
  st.stack->next = NULL;
}

Here's a really simple implementation:

Code:

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

typedef struct node
{
 int data;
 struct node *next;
} Node, *NodePtr;

typedef struct
{
  NodePtr stack;
} Stack, *StackPtr;

void stack_init(StackPtr st)
{
  st->stack = NULL;
}

void push(StackPtr st, int val)
{
  NodePtr new;

  if(!(new = malloc(sizeof(Node))))
  {
    puts("Memory allocation error!");
    return;
  }

  new->data = val;
  new->next = st->stack;
  st->stack = new;
}

int pop(StackPtr st)
{
  NodePtr node = st->stack;
  int val;

  if(!node)
  {
    puts("Stack underflow!");
    return 0;
  }

  val = node->data;
  st->stack = node->next;
  free(node);

  return val;
}

int main(void)
{
  Stack st;
  int vals[8] = { 86, 10, 37, 42, 7, 231, 53, 29 };
  int i;

  stack_init(&st);

  for(i = 0;i < 8;++i)
    push(&st, vals[i]);

  for(i = 0;i < 8;++i)
    printf("%d\n", pop(&st));

  return 0;
}

itsme@dreams:~/C$ ./stack
29
53
231
7
42
37
10
86
itsme@dreams:~/C$