大小端ENDIAN 的检测

1.通过预定义的宏来决定平台的大小端

// The wire format uses a little endian encoding (since that's efficient for
// the common platforms).
#if !defined(FLATBUFFERS_LITTLEENDIAN)
  #if defined(__GNUC__) || defined(__clang__)
    #ifdef __BIG_ENDIAN__
      #define FLATBUFFERS_LITTLEENDIAN 0
    #else
      #define FLATBUFFERS_LITTLEENDIAN 1
    #endif // __BIG_ENDIAN__
  #elif defined(_MSC_VER)
    #if defined(_M_PPC)
      #define FLATBUFFERS_LITTLEENDIAN 0
    #else
      #define FLATBUFFERS_LITTLEENDIAN 1
    #endif
  #else
    #error Unable to determine endianness, define FLATBUFFERS_LITTLEENDIAN.
  #endif
#endif // !defined(FLATBUFFERS_LITTLEENDIAN)

2.运行时检测对宏的大小端判断是否正确

inline void EndianCheck() {
  int endiantest = 1;
  // If this fails, see FLATBUFFERS_LITTLEENDIAN above.
  assert(*reinterpret_cast<char *>(&endiantest) == FLATBUFFERS_LITTLEENDIAN);
  (void)endiantest;
}