macos 64 bit

$ clang -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/ test.c && ./a.out
int                  : 4
unsigned int         : 4
long                 : 8
unsigned long        : 8
size_t               : 8
ssize_t              : 8
off_t                : 8
wchar_t              : 4

test.c

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/types.h>

#define TYPE(type) printf("%-20s : %li\n", #type, sizeof(type))

int main(int n, char **argc) {
  TYPE(int);
  TYPE(unsigned int);
  TYPE(long);
  TYPE(unsigned long);
  TYPE(size_t);
  TYPE(ssize_t);
  TYPE(off_t);
  TYPE(wchar_t);
  return 0;
  return sizeof(size_t);
}