As you mention, the fundamental integer types have guaranteed minimum sizes (or pedantically a range that matches the following sizes if twos' complement is us

As you mention, the fundamental integer types have guaranteed minimum sizes (or pedantically a range that matches the following sizes if twos' complement is used): * >=8 bits: char (CHAR_BIT is exactly 8 in POSIX) * >=16 bits: short and int * >=32 bits: long * >=64 bits: long long The C99 typedefs like uint16_t have to be chosen internally to be one of the underlying types. For those sizes that have no matching underlying type, the implementation will omit typedefs. However don't forget the more flexible C99 typedefs int_leastN_t and int_fastN_t. They both will give you a type of at least N bits, where the "fast" one chooses whichever type is most convenient for the processor, and the "least" version picks whichever is smallest. (For instance int_least16_t is probably short, and int_fast16_t is probably int.)