problem when trying to empty a stack in c

(probably it's a stupid thing but) I have a problem with a stack implementation in C language, when I try to empty it, the function to e开发者_StackOverflow中文版mpty the stack does an infinite loop.. the top of the stack is never null. where I commit an error? thanks bye!

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

typedef struct stack{
  size_t a;
  struct stack *next;
} stackPos;

typedef stackPos *ptr;

void push(ptr *top, size_t a){
    ptr temp;
    temp = malloc(sizeof(stackPos));
    temp->a = a;
    temp->next = *top;
    *top = temp;
}

void freeStack(ptr *top){
    ptr temp = *top;
    while(*top!=NULL){
        //the program does an infinite loop
        *top = temp->next;
        free(temp);
    }
}

int main(){
    ptr top = NULL;
    push(&top, 4);
    push(&top, 8);
    //down here the problem
    freeStack(&top);
    return 0;
}

You're free()ing the same temp variable every time in the loop, so who knows what'll happen, you also need to update temp after you've changed top, so update temp inside your loop e.g. like so:

void freeStack(ptr *top){

  while(*top!=NULL){
       ptr temp = *top;
      *top = temp->next;
      free(temp);
   }
  }

You are not incrementing temp pointer. You are missing temp = temp->next