stack.c

/* a facility for saving pointers in a push pop stack */

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

/* private functions */
STACK *stack_new();
int stack_print();

STACK *stack_new()
{
    STACK *tmp;
    tmp = (STACK *) malloc(sizeof(STACK));
    tmp->saved = NULL;
    tmp->next = NULL;
    tmp->count = 0;
    return(tmp);
}

int stack_depth(STACK **stack)
{
    if (*stack == NULL) {
        return(0);
    } else {
	return((*stack)->count);
    }
}

void stack_push(STACK **stack, char *pointer)
{
    STACK *tmp;
    tmp = stack_new();
    tmp->saved = pointer;

    if (*stack == NULL) {	/* first call */
	tmp->next = NULL;
	tmp->count = 1;
    } else {			/* subsequent calls */
        tmp->next = *stack;	
	tmp->count = (*stack)->count+1;
    }
    *stack = tmp;
    /* stack_print(stack);  */
}

char *stack_pop(STACK **stack)
{

    char *s;
    STACK *tmp;

    if (*stack == NULL) {	/* empty stack */
	return(NULL);
    } else {			/* subsequent calls */
	tmp = *stack;
	s = (*stack)->saved;
	*stack = (*stack)->next;
	free(tmp);
	return(s);
    }
}

void stack_free(STACK **stack) 
{

     STACK *s;

     if (*stack == NULL) {
     	return;
     }
     while ((s=(STACK *)stack_pop(stack)) != NULL) {
         ;
     }
}

int stack_print(STACK **stack) 
{
     int i=0;
     STACK *sp;

     if (stack == NULL) {
     	return(0);
     }
     sp = *stack;
     while(sp != NULL) {
	 if (sp->saved != NULL) {
	     printf("stack #%d: %s\n", i++, sp->saved);
	 }
	 sp = sp->next;
     }
     return(0);
}

char *stack_top(STACK **stack) 		/* return top of stack w/o pop */
{
     char *p;


     if (*stack == NULL) {
     	return NULL;
     }
     if (*stack != NULL) {
	 p = (*stack)->saved;
     } else {
	 p = NULL;
     }
     return p;
}
     

char *stack_walk(STACK **stack)		/* each call returns a new entry, modifies stack */ 
{
     char *p;
     if (*stack == NULL) {
     	return NULL;
     }
     if (*stack != NULL) {
	 p = (*stack)->saved;
	 *stack = (*stack)->next;
     }
     return p;
}

/*
int main() {

    STACK *stack;
    STACK *tmp;
    char *s;

    stack=NULL;
    stack_push(&stack, "hello");
    stack_push(&stack, "world");
    stack_push(&stack, "this");
    stack_push(&stack, "is");
    stack_push(&stack, "a");
    stack_push(&stack, "test");

    tmp=stack;
    while (tmp!=NULL) {
       printf("%s\n", stack_walk(&tmp));
    }

    while ((s=stack_pop(&stack))!=NULL) {
	    printf("%s\n",s);
    }

    return(1);
}
*/