Я не могу сейчас проверить, но мне кажется, это во всех стандартах было, в той или иной формулировке. UPD: нашел драфт С89, а там
Character --- a single byte representing a member of the basic character set of either the source or the execution environment.
...
The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand, which is not itself evaluated. The result is an integer constant.
When applied to an operand that has type char , unsigned char , or signed char , (or a qualified version thereof) the result is 1.
no subject
UPD: нашел драфт С89, а там
Character --- a single byte representing a member of the basic character
set of either the source or the execution environment.
...
The sizeof operator yields the size (in bytes) of its operand,
which may be an expression or the parenthesized name of a type. The
size is determined from the type of the operand, which is not itself
evaluated. The result is an integer constant.
When applied to an operand that has type char , unsigned char , or
signed char , (or a qualified version thereof) the result is 1.