on the use of char

[Matthias Welwarsky]

On Thursday 29 July 2004 04:34, Thiago Macieira wrote:
> George Staikos wrote:
> >   So if your goal is to store a relatively small number and not waste
> > space, can I recommend either using a bitfield int, or thinking again
> > "is it really worth the possible bugs in order to save 3 bytes out
> > of, ex., ~5MB"?
>
> Let me also point out that it would only make sense to use char (or
> signed char or unsigned char) in a struct, and only when you're careful
> about padding.
>
> Using 'char' on the stack or on heap won't help you because variables
> will be 4-byte aligned (or more) anyways. So you get 4 bytes allocated
> despite the fact that you're using 'char'.
>
> If you write a struct like this:
> 	struct {
> 		char small;
> 		int large;
> 		int large2;
> 	};
>
> then the struct is also 12 bytes in size and you're gaining NO space by
> using char, at all.

plus, on any architecture that has no means to access registers "char"-wise 
(i.e. most RISC), the compiler automatically adds code to mask the 
appropriate part of a register, if a char is involved in arithmetic 
operations. On ARM, something like

	for (char i=0; i < 1000; i++)
		bla;

just does not make sense, except for burning cycles.

So not only you don't gain any memory space, you also add a performance 
penalty on many platforms. Of course this is mood since KDE mostly runs on 
ia32/ia64, but theres still PPC, Sparc, a.s.o...

So char makes sense if you need to have bytewise access to something, or to 
represent large memory quantities, but it's inherently slow.

regards,
	matze