stack.c

#include "monty.h"

/**
 * op_stack - set stack mode to last-in first-out (default)
 * @pStack: stack pointer
 */
void op_stack(stack_t **pStack __attribute__((unused)))
{
	op_env.mode = LIFO;
}


/**
 * op_pop - remove the element at the top of the stack
 * @pStack: stack pointer
 */
void op_pop(stack_t **pStack)
{
	stack_t *top = NULL;

	if (!*pStack)
		print_err("L%u: can't pop an empty stack\n", op_env.lineno);

	if (*pStack != (*pStack)->prev)
	{
		top = (*pStack)->prev;
		(*pStack)->next->prev = top;
		top->next = (*pStack)->next;
	}
	free(*pStack);
	*pStack = top;
}


/**
 * op_push - push an element onto the stack
 * @pStack: stack pointer
 */
void op_push(stack_t **pStack)
{
	stack_t *new = NULL;
	const char *nstr = op_env.argv[1];

	if (!(nstr && isinteger(nstr)))
		print_err("L%u: usage: push integer\n", op_env.lineno);

	new = malloc(sizeof(*new));
	if (!new)
		print_err("Error: malloc failed\n");

	new->n = atoi(nstr);
	if (*pStack)
	{
		new->prev = (*pStack);
		new->next = (*pStack)->next;
		new->next->prev = new;
		(*pStack)->next = new;
		if (op_env.mode == LIFO)
			(*pStack) = new;
	}
	else
	{
		new->prev = new;
		new->next = new;
		(*pStack) = new;
	}
}


/**
 * free_stack - free and nullify a stack
 * @pStack: pointer to a pointer to the top of a stack
 */
void free_stack(stack_t **pStack)
{
	stack_t *top = NULL;

	if (pStack && *pStack)
	{
		top = *pStack;
		top->next->prev = NULL;
		do {
			*pStack = top->prev;
			free(top);
		} while ((top = *pStack));
	}
}


/**
 * free_env - clear stack operation environment
 */
void free_env(void)
{
	free_stack(&op_env.sp);
	free(op_env.argv);
	free(op_env.line);
	op_env.argv = NULL;
	op_env.line = NULL;
}