A.1 islittlendian.c

If you want to find out, possibly as part of a script, whether a particular platform is big- or little-endian, the information will probably be squirrelled away somewhere in the headers for the compiler you're using, unfortunately not in any standard way. However, a portable way of doing this (which incidentally illustrates the contrast between the two systems) is to use this little program. It isn't bullet-proof, but if it fails, this is probably the least of your cross-platform problems. You can use the program as follows:

% echo '#define BIGENDIAN' \
    `if ./islittleendian; then echo 0; else echo 1; fi` >bytesex.h

main () {
    /* Are we little or big endian?  Originally from Harbison and Steele. */
    union
    {
	long l;
	char c[sizeof(long)];
    } u;
    u.l = 1;
    exit (u.c[sizeof(long)-1] == 1);
    /* Return 0 (success) if we're little-endian, or 1 (fail) if big-endian */
}