实现

#include <byteswap.h>
#include <stdint.h>


/**
 * @brief 8字节类型的字节序转化
 */
template<class T>
typename std::enable_if<sizeof(T) == sizeof(uint64_t), T>::type
byteswap(T value) {
    return (T)bswap_64((uint64_t)value);
}

/**
 * @brief 4字节类型的字节序转化
 */
template<class T>
typename std::enable_if<sizeof(T) == sizeof(uint32_t), T>::type
byteswap(T value) {
    return (T)bswap_32((uint32_t)value);
}

/**
 * @brief 2字节类型的字节序转化
 */
template<class T>
typename std::enable_if<sizeof(T) == sizeof(uint16_t), T>::type
byteswap(T value) {
    return (T)bswap_16((uint16_t)value);
}

使用系统的函数api就可以实现，为啥要自己写呢？

更好用的跨平台大小端转换

// 定义各个平台之间的大小端转换方式

/*
 * librdkafka - Apache Kafka C library
 *
 * Copyright (c) 2012-2015 Magnus Edenhill
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#ifndef _ENDIANPORTABLE_H_
#define _ENDIANPORTABLE_H_

/**
 * Provides portable endian-swapping macros/functions.
 *
 *   be64toh()
 *   htobe64()
 *   be32toh()
 *   htobe32()
 *   be16toh()
 *   htobe16()
 *   le64toh()
 */

#ifdef __FreeBSD__
  #include <sys/endian.h>
#elif defined __GLIBC__
  #include <endian.h>
 #ifndef be64toh
   /* Support older glibc (<2.9) which lack be64toh */
  #include <byteswap.h>
  #if __BYTE_ORDER == __BIG_ENDIAN
   #define be16toh(x) (x)
   #define be32toh(x) (x)
   #define be64toh(x) (x)
   #define le64toh(x) __bswap_64 (x)
   #define le32toh(x) __bswap_32 (x)
  #else
   #define be16toh(x) __bswap_16 (x)
   #define be32toh(x) __bswap_32 (x)
   #define be64toh(x) __bswap_64 (x)
   #define le64toh(x) (x)
   #define le32toh(x) (x)
  #endif
 #endif

#elif defined __CYGWIN__
 #include <endian.h>
#elif defined(WIN32) || defined(WINx64)
#include <winsock2.h>
 #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)
 #else
  #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)
 #endif
#elif defined __BSD__
  #include <sys/endian.h>
#elif defined sun
  #include <sys/byteorder.h>
  #include <sys/isa_defs.h>
#define __LITTLE_ENDIAN 1234
#define __BIG_ENDIAN 4321
#ifdef _BIG_ENDIAN
#define __BYTE_ORDER __BIG_ENDIAN
#define be64toh(x) (x)
#define be32toh(x) (x)
#define be16toh(x) (x)
#define le16toh(x) ((uint16_t)BSWAP_16(x))
#define le32toh(x) BSWAP_32(x)
#define le64toh(x) BSWAP_64(x)
# else
#define __BYTE_ORDER __LITTLE_ENDIAN
#define be64toh(x) BSWAP_64(x)
#define be32toh(x) ntohl(x)
#define be16toh(x) ntohs(x)
#define le16toh(x) (x)
#define le32toh(x) (x)
#define le64toh(x) (x)
#define htole16(x) (x)
#define htole64(x) (x)
#endif /* sun */

#elif defined __APPLE__
  #include <machine/endian.h>
  #include <libkern/OSByteOrder.h>
#if __DARWIN_BYTE_ORDER == __DARWIN_BIG_ENDIAN
#define be64toh(x) (x)
#define be32toh(x) (x)
#define be16toh(x) (x)
#define le16toh(x) OSSwapInt16(x)
#define le32toh(x) OSSwapInt32(x)
#define le64toh(x) OSSwapInt64(x)
#else
#define be64toh(x) OSSwapInt64(x)
#define be32toh(x) OSSwapInt32(x)
#define be16toh(x) OSSwapInt16(x)
#define le16toh(x) (x)
#define le32toh(x) (x)
#define le64toh(x) (x)
#endif

#elif defined(_MSC_VER)
#include <intrin.h>

#define be64toh(x) _byteswap_uint64(x)
#define be32toh(x) _byteswap_ulong(x)
#define be16toh(x) _byteswap_ushort(x)
#define le16toh(x) (x)
#define le32toh(x) (x)
#define le64toh(x) (x)

#elif defined _AIX      /* AIX is always big endian */
#define be64toh(x) (x)
#define be32toh(x) (x)
#define be16toh(x) (x)
#define le32toh(x)                              \
        ((((x) & 0xff) << 24) |                 \
         (((x) & 0xff00) << 8) |                \
         (((x) & 0xff0000) >> 8) |              \
         (((x) & 0xff000000) >> 24))
#define le64toh(x)                               \
        ((((x) & 0x00000000000000ffL) << 56) |   \
         (((x) & 0x000000000000ff00L) << 40) |   \
         (((x) & 0x0000000000ff0000L) << 24) |   \
         (((x) & 0x00000000ff000000L) << 8)  |   \
         (((x) & 0x000000ff00000000L) >> 8)  |   \
         (((x) & 0x0000ff0000000000L) >> 24) |   \
         (((x) & 0x00ff000000000000L) >> 40) |   \
         (((x) & 0xff00000000000000L) >> 56))
#else
 #include <endian.h>
#endif



/*
 * On Solaris, be64toh is a function, not a macro, so there's no need to error
 * if it's not defined.
 */
#if !defined(__sun) && !defined(be64toh)
#error Missing definition for be64toh
#endif

#ifndef be32toh
#define be32toh(x) ntohl(x)
#endif

#ifndef be16toh
#define be16toh(x) ntohs(x)
#endif

#ifndef htobe64
#define htobe64(x) be64toh(x)
#endif
#ifndef htobe32
#define htobe32(x) be32toh(x)
#endif
#ifndef htobe16
#define htobe16(x) be16toh(x)
#endif

#ifndef htole32
#define htole32(x) le32toh(x)
#endif

#endif /* _ENDIANPORTABLE_H_ */