No. C allows the implementation(A C compiler) to create an internal integer type that is none of the standard integer types and alias that to (u)intX_t , using

No. C allows the implementation(A C compiler) to create an internal integer type that is none of the standard integer types and alias that to (u)intX_t , using an implementation defined mechanism other than typedef. Or it could use a typedef .e.g typedef __special_u8 uint8_t; where the particular compiler internally knows about __special_u8 and treats it differently from unsigned char.