Does an OCaml char represent exactly 8 bits?

Question

From the Char library documentation, I see that chars are able to represent at least the ISO/IEC 8859-1 character set, a character set that uses 8 bits per character. Do OCaml chars represent exactly 8 bits, no more and no less? Where is this documented?

Answer 1

The representation of the char type could be different depending on the implementation of the OCaml language and runtime. While all chars shall fit into 8 bits, an implementation may use a bigger type to represent it. The Char abstraction guarantees that it is impossible to create a character that uses more than 8 bits. And even though the INRIA implementation of OCaml represents Char.t the same as Int.t, it still relies on the assumption that char will fit into 8 bits. For example, a bigarray of n chars will take n bytes. And String.t will have a size in bytes proportional to the number of characters that comprise the string. Last but not least, various external (i.e., implemented in C) functions and the optimized compiler itself will assume that a character fits into 8 bits.