Unless you re writing code that could be useful on a DSP, you re completely entitled to assume bytes are 8 bits. All the world may not be a VAX (or an Intel), but all the world has to communicate, share data, establish common protocols, and so on. We live in the internet age built on protocols built on octets, and any C implementation where bytes are not octets is going to have a really hard time using those protocols.

It s also worth noting that both POSIX and Windows have (and mandate) 8-bit bytes. That covers 100% of interesting non-embedded machines, and these days a large portion of non-DSP embedded systems as well.

From Wikipedia:

The size of a byte was at first selected to be a multiple of existing teletypewriter codes, particularly the 6-bit codes used by the U.S. Army (Fieldata) and Navy. In 1963, to end the use of incompatible teleprinter codes by different branches of the U.S. government, ASCII, a 7-bit code, was adopted as a Federal Information Processing Standard, making 6-bit bytes commercially obsolete. In the early 1960s, AT&T introduced digital telephony first on long-distance trunk lines. These used the 8-bit µ-law encoding. This large investment promised to reduce transmission costs for 8-bit data. The use of 8-bit codes for digital telephony also caused 8-bit data "octets" to be adopted as the basic data unit of the early Internet.

As an average programmer on mainstream platforms, you do not need to worry too much about one byte not being 8 bit. However, I d still use the CHAR_BIT constant in my code and assert (or better static_assert) any locations where you rely on 8 bit bytes. That should put you on the safe side.

(I am not aware of any relevant platform where it doesn t hold true).

Firstly, the number of bits in char does not formally depend on the "system" or on "machine", even though this dependency is usually implied by common sense. The number of bits in char depends only on the implementation (i.e. on the compiler). There s no problem implementing a compiler that will have more than 8 bits in char for any "ordinary" system or machine.

Secondly, there are several embedded platforms where sizeof(char) == sizeof(short) == sizeof(int) , each having 16 bits (I don t remember the exact names of these platforms). Also, the well-known Cray machines had similar properties with all these types having 32 bits in them.

I do a lot of embedded and currently working on DSP code with CHAR_BIT of 16

In history, there s existed a bunch of odd architectures that where not using native word sizes that where multiples of 8. If you ever come across any of these today, let me know.

• The first commerical CPU by Intel was the Intel 4004 (4-bit)
• PDP-8 (12-bit)

The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size.

It might just be a good thing to keep in mind if your doing lots of embedded stuff.

http://en.wikipedia.org/wiki/HP_Saturn_%28microprocessor%29”rel=“nofollow”HP Saturn:

涡轮机的构造是不可磨灭的;即,核心数据单位是4个轨道,可以拥有1个双编码编码的精子。