How can one portably perform pointer arithmetic with single byte precision?
Keep in mind that:
char
is not 1 byte on all platformssizeof(void) == 1
is only available as an extension in GCCYour assumption is flawed - sizeof(char)
is defined to be 1 everywhere.
From the C99 standard (TC3), in section 6.5.3.4 ("The sizeof operator"):
(paragraph 2)
The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type.
(paragraph 3)
When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1.
When these are taken together, it becomes clear that in C, whatever size a char is, that size is a "byte" (even if that's more than 8 bits, on some given platform).
A char
is therefore the smallest addressable type. If you need to address in units smaller than a char
, your only choice is to read a char
at a time and use bitwise operators to mask out the parts of the char
that you want.