Maximum size of size_t

问题

I know in C return type of sizeof operator is size_t being unsigned integer type defined in <stdint.h>. Which means max size of it should be 65535 as stated in C99 standard 7.18.3:

limit of size_t
  SIZE_MAX             65535

However in gcc-4.8.2 header file stdint.h has defined its size much greater than 65535 contradicting to which is stated in C99 standard as below shown,

/* Limit of `size_t' type.  */
# if __WORDSIZE == 64
#  define SIZE_MAX              (18446744073709551615UL)
# else
#  define SIZE_MAX              (4294967295U)
# endif

Kindly help me in understanding why there is a difference or reason behind my misinterpretation.

回答1:

The standard says that SIZE_MAX must be at least 65535.

It specifies no upper bound, and gcc's implementation is perfectly valid.

Quoting the reference you cited (emphasis added):

Its implementation-defined value shall be equal to or greater in magnitude (absolute value) than the corresponding value given below, with the same sign.

来源：https://stackoverflow.com/questions/22514803/maximum-size-of-size-t