c++32位系统和64位系统中类型的字节区别

Type	Type's size on x32 / x64 platform	Note
int	32 / 32	Basic type. On 64-bit systems remains 32-bit.
long	32 / 32	Basic type. On 64-bit Windows systems remains 32-bit. Keep in mind that in 64-bit Linux systems this type was extended to 64-bit. Don't forget about it if you develop code which should be compiled for Windows and Linux systems.
size_t	32 / 64	Basic unsigned type. The type's size is chosen in such a way that you could write the maximum size of a theoretically possible array into it. You can safely put a pointer into size_t type (except for pointers to class functions, but this is a special case).
ptrdiff_t	32 / 64	Similar to size_t type but this is a signed type. The result of the expression where one pointer is subtracted from the other (ptr1-ptr2) will have ptrdiff_t type.
Pointer	32 / 64	The size of the pointer directly depends on the platform's size. Be careful while converting pointers to other types.
__int64	64 / 64	Signed 64-bit type.
DWORD	32 / 32	32-bit unsigned type. In WinDef.h is defined as:typedef unsigned long DWORD;
DWORDLONG	64 / 64	64-bit unsigned type. In WinNT.h is defined as:typedef ULONGLONG DWORDLONG;
DWORD_PTR	32 / 64	Unsigned type in which a pointer can be placed. In BaseTsd.h is defined as:typedef ULONG_PTR DWORD_PTR;
DWORD32	32 / 32	32-bit unsigned type. In BaseTsd.h is defined as:typedef unsigned int DWORD32;
DWORD64	64 / 64	64-bit unsigned type. In BaseTsd.h is defined as:typedef unsigned __int64 DWORD64;
HALF_PTR	16 / 32	A half of a pointer. In Basetsd.h is defined as:#ifdef _WIN64 typedef int HALF_PTR;#else typedef short HALF_PTR;#endif
INT_PTR	32 / 64	Signed type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef __int64 INT_PTR; #else typedef int INT_PTR;#endif
LONG	32 / 32	Signed type which remained 32-bit. That's why in many cases LONG_PTR now should be used. In WinNT.h is defined as:typedef long LONG;
LONG_PTR	32 / 64	Signed type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef __int64 LONG_PTR; #else typedef long LONG_PTR;#endif
LPARAM	32 / 64	Parameter for sending messages. In WinNT.h is defined as:typedef LONG_PTR LPARAM;
SIZE_T	32 / 64	Analog of size_t type. In BaseTsd.h is defined as:typedef ULONG_PTR SIZE_T;
SSIZE_T	32 / 64	Analog of ptrdiff_t type. In BaseTsd.h is defined as:typedef LONG_PTR SSIZE_T;
ULONG_PTR	32 / 64	Unsigned type in which a pointer can be placed. In BaseTsd.h is defined as:#if defined(_WIN64) typedef unsigned __int64 ULONG_PTR;#else typedef unsigned long ULONG_PTR;#endif
WORD	16 / 16	Unsigned 16-bit type. In WinDef.h is defined as:typedef unsigned short WORD;
WPARAM	32 / 64	Parameter for sending messages. In WinDef.h is defined as:typedef UINT_PTR WPARAM;

中文版

类型  32位 64位

int    32    32

char 8     8

long 32  32

指针 32  64 

例题：

64位操作系统，不同类型变量对应的字节数为：（红色的表示与32位系统不同之处）

        char ：1个字节  
      char*(即指针变量): 8个字节 
      short int : 2个字节  
      int：  4个字节  
      unsigned int : 4个字节  
      float:  4个字节  
      double:    8个字节  
      long:   8个字节 
      long long:  8个字节  
      unsigned long:  8个字节 

64位系统在内存管理方面遵循8字节对齐，原则：在8字节对齐的情况下，按8个字节为单位分配存储空间，如果不足，会自动补充，本次分配不足以存放下面的变量时，会重新分配空间。

structA{
   unsigned int a; //对于开始连续的第一个8字节内存，a占4字节
   char b[2];      //b[]占1*2字节，在a后的连续2字节内存放，还剩2个字节，
   double c;       //c占8字节，第一个8字节还剩2字节不足以存放c,自动补充该2字节。并同时开辟第二个8字节内存存放c
   short d;        //d占2字节，开辟第三个8字节，存放d。剩余的6个字节补齐。故总共开辟了8*3=24字节存放该数据结构
}