This provides the endian conversion functions form endian.h on Windows, Linux, *BSD, Mac OS X, and QNX. You still need to use -std=gnu99 instead of -std=c99 for gcc. The functions might actually be macros. Functions: htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh, htobe64, htole64, be64toh, le64toh. License: I hereby put …

portable_endian.h

// "License": Public Domain
// I, Mathias Panzenböck, place this file hereby into the public domain. Use it at your own risk for whatever you like.
// In case there are jurisdictions that don't support putting things in the public domain you can also consider it to
// be "dual licensed" under the BSD, MIT and Apache licenses, if you want to. This code is trivial anyway. Consider it
// an example on how to get the endian conversion functions on different platforms.

#ifndef PORTABLE_ENDIAN_H__
#define PORTABLE_ENDIAN_H__

#if (defined(_WIN16) || defined(_WIN32) || defined(_WIN64)) && !defined(__WINDOWS__)

#	define __WINDOWS__

#endif

#if defined(__linux__) || defined(__CYGWIN__)

#	include <endian.h>

#elif defined(__APPLE__)

#	include <libkern/OSByteOrder.h>

#	define htobe16(x) OSSwapHostToBigInt16(x)
#	define htole16(x) OSSwapHostToLittleInt16(x)
#	define be16toh(x) OSSwapBigToHostInt16(x)
#	define le16toh(x) OSSwapLittleToHostInt16(x)
 
#	define htobe32(x) OSSwapHostToBigInt32(x)
#	define htole32(x) OSSwapHostToLittleInt32(x)
#	define be32toh(x) OSSwapBigToHostInt32(x)
#	define le32toh(x) OSSwapLittleToHostInt32(x)
 
#	define htobe64(x) OSSwapHostToBigInt64(x)
#	define htole64(x) OSSwapHostToLittleInt64(x)
#	define be64toh(x) OSSwapBigToHostInt64(x)
#	define le64toh(x) OSSwapLittleToHostInt64(x)

#	define __BYTE_ORDER    BYTE_ORDER
#	define __BIG_ENDIAN    BIG_ENDIAN
#	define __LITTLE_ENDIAN LITTLE_ENDIAN
#	define __PDP_ENDIAN    PDP_ENDIAN

#elif defined(__OpenBSD__)

#	include <endian.h>

#	define __BYTE_ORDER    BYTE_ORDER
#	define __BIG_ENDIAN    BIG_ENDIAN
#	define __LITTLE_ENDIAN LITTLE_ENDIAN
#	define __PDP_ENDIAN    PDP_ENDIAN

#elif defined(__NetBSD__) || defined(__FreeBSD__) || defined(__DragonFly__)

#	include <sys/endian.h>

#	define be16toh(x) betoh16(x)
#	define le16toh(x) letoh16(x)

#	define be32toh(x) betoh32(x)
#	define le32toh(x) letoh32(x)

#	define be64toh(x) betoh64(x)
#	define le64toh(x) letoh64(x)

#elif defined(__WINDOWS__)

#	include <winsock2.h>
#	ifdef __GNUC__
#		include <sys/param.h>
#	endif

#	if BYTE_ORDER == LITTLE_ENDIAN

#		define htobe16(x) htons(x)
#		define htole16(x) (x)
#		define be16toh(x) ntohs(x)
#		define le16toh(x) (x)
 
#		define htobe32(x) htonl(x)
#		define htole32(x) (x)
#		define be32toh(x) ntohl(x)
#		define le32toh(x) (x)
 
#		define htobe64(x) htonll(x)
#		define htole64(x) (x)
#		define be64toh(x) ntohll(x)
#		define le64toh(x) (x)

#	elif BYTE_ORDER == BIG_ENDIAN

		/* that would be xbox 360 */
#		define htobe16(x) (x)
#		define htole16(x) __builtin_bswap16(x)
#		define be16toh(x) (x)
#		define le16toh(x) __builtin_bswap16(x)
 
#		define htobe32(x) (x)
#		define htole32(x) __builtin_bswap32(x)
#		define be32toh(x) (x)
#		define le32toh(x) __builtin_bswap32(x)
 
#		define htobe64(x) (x)
#		define htole64(x) __builtin_bswap64(x)
#		define be64toh(x) (x)
#		define le64toh(x) __builtin_bswap64(x)

#	else

#		error byte order not supported

#	endif

#	define __BYTE_ORDER    BYTE_ORDER
#	define __BIG_ENDIAN    BIG_ENDIAN
#	define __LITTLE_ENDIAN LITTLE_ENDIAN
#	define __PDP_ENDIAN    PDP_ENDIAN

#elif defined(__QNXNTO__)

#	include <gulliver.h>

#	define __LITTLE_ENDIAN 1234
#	define __BIG_ENDIAN    4321
#	define __PDP_ENDIAN    3412

#	if defined(__BIGENDIAN__)

#		define __BYTE_ORDER __BIG_ENDIAN

#		define htobe16(x) (x)
#		define htobe32(x) (x)
#		define htobe64(x) (x)

#		define htole16(x) ENDIAN_SWAP16(x)
#		define htole32(x) ENDIAN_SWAP32(x)
#		define htole64(x) ENDIAN_SWAP64(x)

#	elif defined(__LITTLEENDIAN__)

#		define __BYTE_ORDER __LITTLE_ENDIAN

#		define htole16(x) (x)
#		define htole32(x) (x)
#		define htole64(x) (x)

#		define htobe16(x) ENDIAN_SWAP16(x)
#		define htobe32(x) ENDIAN_SWAP32(x)
#		define htobe64(x) ENDIAN_SWAP64(x)

#	else

#		error byte order not supported

#	endif

#	define be16toh(x) ENDIAN_BE16(x)
#	define be32toh(x) ENDIAN_BE32(x)
#	define be64toh(x) ENDIAN_BE64(x)
#	define le16toh(x) ENDIAN_LE16(x)
#	define le32toh(x) ENDIAN_LE32(x)
#	define le64toh(x) ENDIAN_LE64(x)

#else

#	error platform not supported

#endif

#endif

thinking again - your code might work perfectly for GNU C on the windows platform.
guess what - people are trying out to compile it with MSVC - and its just not documented that you were not targeting that compiler.

Defining __WINDOWS__ is not good. #ifdef __WINDOWS__ can work differently in files that include and don't include endian.h, which would be surprising. It's better to define symbols that communicate their limited scope, e.g. __ENDIAN_WINDOWS.
The use of __builtin_bswapNN whould be limited to the compiles that define it (GCC and Clang, both define __GNUC__).

This header is useful. I want to create a conan package. Counld you please create a repo for this gist to support a better version control?

I haven't updated this in 6 years, I think it's save to say there won't be any new version of this. I'm not maintaining it. 😄
Just copy the file/code wherever you need it. I really don't see the benefit of a full repo for that. All that would do is people writing issues that I don't feel like fixing. A gist makes clear its just an example on how one can do something like this.

There is currently no support for QNX Neutrino. You can add it easily as shown below:

#elif defined(__QNXNTO__)

#	include <gulliver.h>