c - Why did POSIX mandate CHAR_BIT==8?

Question

There's a note in the POSIX rationale that mandating CHAR_BIT be 8 was a concession made that was necessary to maintain alignment with C99 without throwing out sockets/networking, but I've never seen the explanation of what exactly the conflict was. Does anyone have anecdotes or citations for why it was deemed necessary?

Edit: I've gotten a lot of speculative answers regarding why it's desirable for CHAR_BIT to be 8, and I agree, but what I'm really looking for is what the technical conflict between C99 and the networking stuff in POSIX is. My best guess is that it has something to do with C99 requiring uint*_t to be exact-sized types (no padding) whereas the inttypes.h previously in POSIX made no such requirement.

Answer 1

Because the vast majority of standards (related to communication) out of ANSI and ISO talk in terms of octets (8-bit values). There is none of that wishy-washy variable-sized character nonsense :-)

And, since a rather large quantity of C code used char or unsigned char for storing and/or manipulating these values, and assumed they were 8 bits wide, the fact that ISO allowed a variable size would cause problems for that code.

Remember one of the over-riding goals of ISO C - existing code is important, existing implementations are not. This is one reason why limits.h exists in the first place rather than just assuming specific values, because there was code around that assumed otherwise.

POSIX also followed that same guideline. By mandating a byte size of 8 bits, they prevented the breakage of a huge amount of code already in the real world.