A simple but effective Stack structure in C for School projects.

stack.c

#include <stdlib.h>
#include <string.h>

#include "stack.h"


Stack *stack_new(Stack *st, size_t size, bool (*equals)(const void*, const void*))
{
	if (size <= 0) return NULL;
	st->idx    = 0;
	st->max    = size;
	st->data   = salloc(size, sizeof(*st->data), false);
	st->equals = equals;
	return st;
}

size_t stack_size(Stack *st)
{
	return st != NULL ? st->idx : 0;
}

bool stack_is_empty(Stack *st) { return st->idx == 0; }

bool stack_contains(Stack *st, Object key)
{
	if (st->equals == NULL) {
		fprintf(stderr, "%s: equals callback undefined\n", __func__);
		return false;
	}

	for (int idx = 0; idx < stack_size(st); idx++) {
		if (st->equals(st->data[idx], key)) {
			return true;
		}
	}
	return false;
}

void stack_push(Stack *st, Object key)
{
	if (st == NULL) { return; }
	if (st->idx == st->max) { return; }
	if (stack_contains(st, key)) { return; }
	st->data[++st->idx] = key;
}

Object stack_pop(Stack *st)
{
	if (st == NULL) { return NULL; }
	return st->data[st->idx--];
}

void stack_reset(Stack *st)
{
	st->idx = 0;
}

void stack_destroy(Stack *st)
{
	if (st == NULL) { return; }
	free(st->data); st->data = NULL;
	st->idx = st->max = 0;
}

stack.h

#ifndef _STACK_H_
#define _STACK_H_

typedef unsigned char bool;
#define true  1
#define false 0

typedef void* Object;

typedef struct _stack {
	size_t idx, max;
	Object *data;    /* data[idx] = void* */
	bool (*equals)(const void*, const void*);
} Stack;


Stack *stack_new(Stack *st, size_t size, bool (*equals)(const void*, const void*));
size_t stack_size(Stack *st);
bool   stack_is_empty(Stack *st);
bool   stack_contains(Stack *st, Object key);
void   stack_push(Stack *st, Object key);
Object stack_pop(Stack *st);
void   stack_reset(Stack *st);
void   stack_destroy(Stack *st);


#endif