c++ - What platforms have something other than 8-bit char?

Question

Every now and then, someone on SO points out that char (aka 'byte') isn't necessarily 8 bits.

It seems that 8-bit char is almost universal. I would have thought that for mainstream platforms, it is necessary to have an 8-bit char to ensure its viability in the marketplace.

Both now and historically, what platforms use a char that is not 8 bits, and why would they differ from the "normal" 8 bits?

When writing code, and thinking about cross-platform support (e.g. for general-use libraries), what sort of consideration is it worth giving to platforms with non-8-bit char?

In the past I've come across some Analog Devices DSPs for which char is 16 bits. DSPs are a bit of a niche architecture I suppose. (Then again, at the time hand-coded assembler easily beat what the available C compilers could do, so I didn't really get much experience with C on that platform.)

Answer 1

char is also 16 bit on the Texas Instruments C54x DSPs, which turned up for example in OMAP2. There are other DSPs out there with 16 and 32 bit char. I think I even heard about a 24-bit DSP, but I can't remember what, so maybe I imagined it.

Another consideration is that POSIX mandates CHAR_BIT == 8. So if you're using POSIX you can assume it. If someone later needs to port your code to a near-implementation of POSIX, that just so happens to have the functions you use but a different size char, that's their bad luck.

In general, though, I think it's almost always easier to work around the issue than to think about it. Just type CHAR_BIT. If you want an exact 8 bit type, use int8_t. Your code will noisily fail to compile on implementations which don't provide one, instead of silently using a size you didn't expect. At the very least, if I hit a case where I had a good reason to assume it, then I'd assert it.