Another set of typedef names for integer types defined in < inttypes.h > is called “fastest minimum-width integer types.” Each of these typedef names designates aninteger type that is usually fastest to operate with among all integer types that have at least the specified width. They have the general form of int_fastn_t or uint_fastn_t where n is the minimum required width. For instance, int_fast32_t is the fastest signed integer type having a width of at least 32 bits. The fastest minimum-width integer types are:

  int_fast8_t      int_fast16_t int_fast32_t     int_fast64_t

Their unsigned counterparts are:

  uint_fast8_t     uint_fast16_t uint_fast32_t    uint_fast64_t

What are these typedef names good for? Suppose you need a loop counter that needs no less than 16 bits. You want to make sure that the counter’s type is always the one with which the current machine’s CPU operates optimally. By using int_fast16_t You ensure that on every platform, the compiler always uses the fastest integral type that has at least 16 bits:

 #include for (int_fast16_t n=0; n<1000; ++n){//.. do something}