Architectures with 2-bytes (or more) atomic endianness

Question

Until recently, I thought that by specifying if an architecture is either big-endian or little-endian we would cover most systems (except middle-endian but these systems are not very common). But then, I read that the endianness "atomics" can be greater than bytes so that these system :

• little endian with 1 byte atomic
• little endian with 2 bytes atomic

will encode integers in different ways.

Question: How common systems with atomics equal or greater than two are?

Additional questions

• Can the atomic size depends on the type of integer (for example different atomics for uint32_t and uint64_t )?
• Do I have the guarantee that a char is always 1-byte long even on system with 2-bytes endianness atomics?

Answer 1

If you need to worry about the particular native byte order of your machine, you can use functions such as ntohl() and ntohs() , or just read one byte at a time.

There isn't any guarantee that char is exactly 8 bits wide (see <limits.h> to check the number), but char is guaranteed to be at least 8 bits wide (so that a char[] can hold a UTF-8 string) and sizeof(char) is guaranteed to be 1. If you need an exact 8-bit-wide type, use uint8_t .