/**
* slibc — Yet another C library
* Copyright © 2015, 2016 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef _STDDEF_H
#define _STDDEF_H
#include <slibc/version.h>
#include <slibc/features.h>
/**
* `NULL` is a zero-values constant, conventionally
* a `void`-pointer (it is specified this way in
* POSIX, it does not really matter as long as it has
* the same width and ISO C does not specify it this
* way), use to indicate that a pointer does not point
* to anything.
*
* Note on considerations of `NULL` being harmful:
* It is important to remember than `sizeof(NULL)`
* does not equal `sizeof(int)` on all machines.
* Therefore, in variadic arguments, it is important
* not to substitute `x` for `x != NULL`. This
* would cause horrible bugs. If you insist on not
* using `NULL`, correct substitutions would be
* `!!x` or `x != 0`.
* Note that `NULL` is genuinely harmful in C++,
* but excessive use of C++, and especially it
* features, is harmful too.
*
* Strictly speaking, to deference `NULL` is not an
* illegal action, but the operating system will
* kill you with `SIGSEGV` (segmentation fault or
* acess violation), and makes your you have no reason
* to my never mapping any memory there. However, the
* operating system itself, and programs running
* before the operating system, that is, any program
* not abstracted away from the hardware by virtual
* memory, have use of the address 0.
*
* @etymology Pointer with numerical value (0).
*
* @since Always.
*/
#ifndef NULL
# define NULL ((void*)0)
#endif
/**
* Get the offset of a member in a `struct`, in bytes.
*
* For example. Consider the structure
* ```
* struct example
* {
* char offset_is_0[16];
* char offset_is_16[16];
* }
* ```
* `offsetof(struct example, offset_is_0)` evaluates to
* 0 because it is at the top of the structure.
* `offsetof(struct example, offset_is_16)` evaluates to
* 16 because the member above it in the structure
* has offset 0 and size 16. 0 + 16 = 16.
*
* @etymology Address-(offset of) member.
*
* @param type:identifier The identifier for a structure.
* @param member:identifier The identifier for a member, direct or indirect,
* of the structure.
* @return :size_t The offset of the member.
*
* @since Always.
*/
#define offsetof(type, member) \
((size_t)((char*)&(((type*)NULL)->member) - (char*)NULL))
/* TODO The behaviour of this is undefined, and a builtin function
* shall be used when available. That would also improve diagnostics.
* If compilers that support ({ }), NULL could be replaced with a
* temporary variable, this would only remove the undefined behaviour,
* but any serious compiler should support the current implementation. */
#define __NEED_ptrdiff_t
#define __NEED_wchar_t
#define __NEED_size_t
#if defined(__C11__) || defined(__BUILDING_SLIBC)
# define __NEED_max_align_t
#endif
#include <bits/types.h>
#endif
