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From: Thomas Matelich <tmatelich@zetec.com>
Subject: Re: portable method of determining endianness byte order.
Date: 1999/11/22
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Pukalo Boyd 810-492-3661 wrote:

> I have been trying to find a portable method of determining the
> endianness byte order at compile time
> to produce code that will work properly on both windows and unix
> machines. I have searched the documentation
> i have ( the books on the C Standard Library and the C++ Standard
> Library) and havent found anything. Please help. Any pointers or
> suggestions would be very helpful. Thanks.
>

Here is what I came up with recently for this problem:

 //btw: BIG_ENDIAN -> UNIX hardware, LITTLE_ENDIAN -> x86 hardware
 enum ByteOrdering { BIG_ENDIAN, LITTLE_ENDIAN };

 class EndianNess
 {
 public:
  operator ByteOrdering() const { return byte_ordering; } //implicit
conversion

  friend const EndianNess& Omega();
 private:
  EndianNess()
  {
   //checks the first byte for a one
   //I have verified this to be correct on Windows and HPUX
   unsigned int n = 1;
   char* c;
   c = (char*)&n;
   byte_ordering = (!*c) ? BIG_ENDIAN : LITTLE_ENDIAN;
  }

  ByteOrdering byte_ordering;
 };

 inline const EndianNess& Omega()
 {
  static EndianNess _omega;
  return _omega;
 }


I had my reasons for returning EndianNess instead of ByteOrdering from
Omega, though I cannot think of them now.  This will not work on vax I
believe because it is something besides big or little endian.


Tom Matelich
sosedada@usa.net
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