64-bit Differences

Sample Code

sizes.c

#include <stdio.h>  /* printf   */
#include <stdint.h> /* intptr_t */

int main(void)
{
  int i = 123;       /* sizeof(int) depends on architecture */
  int *p1 = &i;      /* works on all architectures          */
  
  intptr_t j = 456;  /* intptr_t is a pointer-sized int */
  intptr_t *p2 = &j; /* works on all architectures      */
  
  i = (int)p1;       /* Probably works on 32-bit, may not on 64-bit  */
  j = (intptr_t)p2;  /* Will work on either architecture             */

  printf("sizeof(char)        : %lu\n", sizeof(char));
  printf("sizeof(short)       : %lu\n", sizeof(short));
  printf("sizeof(int)         : %lu\n", sizeof(int));
  printf("sizeof(long)        : %lu\n", sizeof(long));
  printf("sizeof(long long)   : %lu\n", sizeof(long long)); /* C99 */
  printf("sizeof(float)       : %lu\n", sizeof(float));
  printf("sizeof(double)      : %lu\n", sizeof(double));
  printf("sizeof(long double) : %lu\n", sizeof(long double));
  printf("sizeof(void*)       : %lu\n", sizeof(void*));
  printf("sizeof(size_t)      : %lu\n", sizeof(size_t));
  printf("sizeof(intptr_t)    : %lu\n", sizeof(intptr_t));

  return 0;
}

Outputs:

32-bit Microsoft/GCC/Cygwin

sizeof(char)        : 1
sizeof(short)       : 2
sizeof(int)         : 4
sizeof(long)        : 4
sizeof(long long)   : 8
sizeof(float)       : 4
sizeof(double)      : 8
sizeof(long double) : 12
sizeof(void*)       : 4
sizeof(size_t)      : 4
sizeof(intptr_t)    : 4

32-bit Clang

sizeof(char)        : 1
sizeof(short)       : 2
sizeof(int)         : 4
sizeof(long)        : 4
sizeof(long long)   : 8
sizeof(float)       : 4
sizeof(double)      : 8
sizeof(long double) : 16
sizeof(void*)       : 4
sizeof(size_t)      : 4
sizeof(intptr_t)    : 4

64-bit Microsoft (LLP64)

sizeof(char)        : 1
sizeof(short)       : 2
sizeof(int)         : 4
sizeof(long)        : 4
sizeof(long long)   : 8
sizeof(float)       : 4
sizeof(double)      : 8
sizeof(long double) : 8
sizeof(void*)       : 8
sizeof(size_t)      : 8
sizeof(intptr_t)    : 8

64-bit MinGW (LLP64)

sizeof(char)        : 1
sizeof(short)       : 2
sizeof(int)         : 4
sizeof(long)        : 4
sizeof(long long)   : 8
sizeof(float)       : 4
sizeof(double)      : 8
sizeof(long double) : 16
sizeof(void*)       : 8
sizeof(size_t)      : 8
sizeof(intptr_t)    : 8

64-bit Clang/GCC (Linux/Mac LP64)

sizeof(char)        : 1
sizeof(short)       : 2
sizeof(int)         : 4
sizeof(long)        : 8
sizeof(long long)   : 8
sizeof(float)       : 4
sizeof(double)      : 8
sizeof(long double) : 16
sizeof(void*)       : 8
sizeof(size_t)      : 8
sizeof(intptr_t)    : 8

Warning:

sizes.c:12:7: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]