At Mon, 03 Jan 2011 00:08:23 -0800, Patrick Horgan wrote:
I'm not so sure. This idiom has been around as long as unions were in C. Do you know of any compilers that don't support it? Of course memcpy or any other solution using character pointers would be supported, but compilers wouldn't generate efficient code for in this case a simple swap of 16 bit ints. Clearly the specs say that a union can only contain one object at a time. Hmmm. The C99 spec has a footnote to section 6.5.2.3/3 that seems to clearly say you can do this The C99 spec is irrelevant to C++; it isn't even "included by reference," as the C89 spec is. Good point Dave, but I think I've let go of it as a possibility for C++ anyway. I'll have to rewrite that part. The C spec also mentions
On 01/03/2011 08:01 AM, Dave Abrahams wrote: things about how non-share parts become undefined when switching to a different member of the union, but since the C++ spec calls for destruction and in place construction to switch, it's clearly out. Patrick