Thread: Big Endian Little Endian Complex- Converting Characters

  1. 07-10-2006 #1
    bd02eagle
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    Big Endian Little Endian Complex- Converting Characters

    I'm reading in a data file which is in little endian format and Im trying to use subroutines to convert int, float, character, etc. into big endian format. I've succeeded in converting the integers from the data file using this subroutine.

    Code:
    int fixint(int *fpt)
{
	unsigned char B1, B2, B3, B4;
	unsigned int swapper;
	B4 = *fpt & 0x000000FF;
	     *fpt >>= 8;	    
	B3 = *fpt & 0x000000FF;
	     *fpt >>= 8;
	B2 = *fpt & 0x000000FF;
	     *fpt >>= 8;
	B1 = *fpt & 0x000000FF;
	     *fpt >>= 8;
		
	swapper = 0;
	swapper += B4;
	swapper <<= 8;
	swapper += B3;
	swapper <<= 8;
	swapper += B2;
	swapper <<= 8;
	swapper += B1;
	*fpt = swapper;
}
    Obviously this only works for integers but I really have no idea where to start with characters or floating point numbers. lol Please help.
  2. 07-10-2006 #2
    Salem
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    Treat everything as an array of bytes and reverse them?

    floats/doubles you will need something like
    Code:
    unsigned char temp[sizeof(double)];
memcpy ( temp, sourceData, sizeof temp );
reverse ( temp, sizeof temp );
memcpy( &myDouble, temp );
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
  3. 07-11-2006 #3
    kris.c
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    More of a general question :
    What is the best method to find out whether my machine uses little endian or big endian ?
  4. 07-11-2006 #4
    Salem
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    The best method is to write code which doesn't care.
    http://c-faq.com/cpp/ifendian.html

    Also, the world isn't totally divided into 'big' and 'little'.
    There are middle-endian machines.
    http://en.wikipedia.org/wiki/Endianness
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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