On Mon, Dec 31, 2001 at 01:33:37PM -0500, Colin Walters wrote: > On Mon, 2001-12-31 at 05:40, Julian Gilbey wrote: > > I believe that the author (Knuth) presumably thought "c should only be > > between 0 and 127, probably not even that far, and we're using c as an > > array index, where we've only allocated 256 chars for this array. > > Right. Then it should be explicitly declared as an "unsigned char". > > > As char might be a signed char, c could feasibly be less than 0, > > Not if you declare it as unsigned explicitly. > > > and there's a small possibility that char could be some weird wide > > character thing, > > No, the C standard guarantees that a char is exactly a single byte; i.e. > sizeof(char) == 1. > > > so c could feasibly be greater than 255, we'll > > perform the checks just check to be on the safe side." Defensive > > programming. > > It can't be larger than 255 (precisely because it is limited to a single > byte). > > The more I think about it, the more it makes sense to always explicitly > declare all char variables as signed or unsigned; otherwise, you're just > asking for latent bugs.
As someone pointed out, a byte is required to contain at least the unsigned 0 - 255 range. It can be larger. A lot of DSP chips support 32-bit access as the basic element. sizeof(char) == sizeof(long) == 1. Or he could have char redefined in a really stupid and non-C-conforming header somewhere someday. Not his fault. Characters intended to contain character data should in fact be 'char' rather tahn explicitly signed. The C library expects them that way; and the default is chosen for increased performance on the architecture in question, generally, or compatibility. -- Daniel Jacobowitz Carnegie Mellon University MontaVista Software Debian GNU/Linux Developer
