The sized types are optional, since they are more restrictive than the ordinary types - see section 7.20.1.1 in the standard (<a href="http:&#x2F;&#x2F;port70.net&#x2F;~nsz&#x2F;c&#x2F;c11&#x2F;n1570.html#7.20.1.1" rel="nofollow">http:&#x2F;&#x2F;port70.net&#x2F;~nsz&#x2F;c&#x2F;c11&#x2F;n1570.html#7.20.1.1</a>). To summarize: intN_t is exactly N bits, with zero padding bits, and 1 2&#x27;s complement sign bit; uintN_t is exactly N bits, with zero padding bits; the implementation must provide such typedefs for all such types it supports.<p>So, if a system is 1&#x27;s complement, you won&#x27;t get the intN_t types at all. If the system doesn&#x27;t support a particular bit width, you won&#x27;t get the types for that width.